One of the best things about having an incomparable super-genius for a Servant was the knowledge that, with enough time to work on a problem, you could fix anything.

And, even twenty-four hours after Berserker's rampage had ended, Fuyuki needed a lot of fixing. Waver hurried, muscles burning, through the suburbs that he'd grown so familiar with over just the last few days – now transformed into a scene from hell. Ash and soot coated every surface, painting the houses a stark, bleak monochrome. Smoke still rose from a dozen places on this street alone, because all the roads were blocked and Berserker had murdered the fire service in any case. Twice today Waver had seen a fire suddenly flare back up out of control, the wind catching it at the wrong moment or a collapsing wall letting in more air.

Trees, uprooted. Telephone poles, thrown to the ground. Rubble, everywhere. Waver had never visited the site of a hurricane or other natural disaster, but he had a television. The resemblance was eerie, and all the more so for thinking that it had been the fault of a single monster. Worse, this carnage had been directed, calculated to cause as much damage as possible, with as little possibility for recovery.

Even in the light of day, the cheer and vibrancy had vanished utterly from the quiet neighbourhood.

Oh, there was life, lots of it. More of it than usual. Every able-bodied citizen was out on the street, doing their part to help with repair – lifting, carrying, clearing away rubble. The elderly and infirm handed out water, or dished out soup from great vats.

There hadn't been any official response, any co-ordination of effort. There couldn't be; Berserker had kneecapped the city to prevent just that. Everything that was happening had been organised locally, ordinary people just pitching in. It could have been a heartening tableau of how humanity pulled together in their worst moments… if it weren't for the charred corpses no-one had yet cleared away, and the grim exhaustion on the faces of the helpers.

And there Waver was, doing nothing but carrying wheelbarrows full of wood and brick to the construction teams, so that people who'd studied useful things like 'how to build a house' could do the real work. He considered mentioning the fact that he was being educated at the finest school of magecraft in the world, and laughed bitterly. What a joke.

If there were fewer magi and more builders, the world would be a better place.

One of the worst things about having an incomparable super-genius for a Servant was the knowledge that you could fix anything but weren't allowed to.

Over there, where smoke was still rising from that house; Caster could snuff out that flame in a heartbeat. No, better, she would probably just reach out with that gauntlet of hers and take it, shift it where it was needed – say, over here, where a half-dead salaryman was trapped inside his crushed car. People were working with tools to prise the door open, but a cutting blowtorch would do the job instantly.

A hundred wounds Caster could heal with a snap of her fingers. A thousand blockages she could sweep away with a wave of her hand. She'd do it, too, if Waver asked. All around, people cried out for help that Waver could give, and he…

… did so very little.

Not nothing. As scrawny as he was, he was still a magus, and subtle Reinforcement meant he could do grunt work all day. Caster, despite her delicate looks, was by far the strongest person here, and was also carrying just enough to not look suspicious.

In the end, that was what it was about. Blending in, keeping the secret, not standing out. There was a rational part of Waver's brain that knew he was making the smart choice. If there was another Servant waiting to prey on the city like Berserker had, Waver would need all the energy he could spare. If the Association found out he'd been openly performing miracles, even for a good cause, not only would Waver be in for it, but any witnesses would need to be silenced as well. Staying subtle was, in the long run, the best way to help.

But it sure didn't feel like it.

Next to him, there was a beep, and Caster nudged his shoulder. Ah. He hadn't been keeping an eye on the time, but clearly she had, or had set an alarm. He looked up at the sky, and yeah, it was starting to get dark. He set his wheelbarrow down, and nodded wordlessly at the construction worker waiting to pick it up. Then, he made his way back to the Mackenzies' house.

For once, Caster was quiet on the way back, making notes as they walked on some kind of electronic pad.

Posing as the Mackenzies' grandson was, on paper, a decent idea – he got lodging and food for free, and a family unit was far more anonymous than a couple was, especially a Western couple and especially one containing someone as flamboyant as Caster. It was a simple job: the Mackenzies already had a grandson, and according to Waver's research he lived in Australia and was unlikely to visit, so all that was needed was to replace their memories of their actual grandson with Waver. That kind of hypnotism was so simple it was hardly magic, and a real magus probably wouldn't have needed it… but it did get the job done.

However, if he was going to take advantage of the fact he had to play the part at least some of the time. With everything that had been going on, Martha Mackenzie had absolutely refused to hear of Waver being out after dark, and her husband had agreed.

So, when he arrived back, he made a point to be as obvious as possible about it.

"Gramps! Granny! I'm back!"

"Oh, Waver! Thank goodness," came an answering call from the kitchen. "Is Lisa still with you?"

Caster – 'Lisa del Giocondo' as far as Waver's hosts were concerned – laughed. "Don't you worry, Ms Mackenzie," she said. "Waver's not getting out of my sight."

"Well, I should think so." Martha Mackenzie emerged from the kitchen to wave a ladle at Waver. She was a tiny, elderly woman, but the Japanese air seemed to agree with her, because she still carried herself with surprising vigor. "You're very lucky to have such an accomplished private tutor, young man, and don't you forget it. Especially one willing to come all this way to teach you, and especially with all the trouble lately, so you look after her! Lisa, dear, you let me know if you need anything, and I'll make sure Glenn or Waver see you right."

"Oh, of course, darling," gushed Caster. "You're ever so generous. But we do need to be off – work never ceases, you know how it is…"

Martha smiled. "Of course. You two go on upstairs, I'll be down here if you need me. Glenn should be back soon."

"Will do!"

And up they went to the spare room, which Waver had taken as his own. More importantly, the room which, shortly afterwards, Caster had taken for her own.

The room was currently the most heavily-warded place in Fuyuki, including the Three Familes' personal workshops and the Kotomine Church.

Intricate formalcraft circuitry done partly in blood and partly in solder covered every inch of the walls, with layer upon layer of circles in the middle of the floor. More circles were crammed into the corners and empty spaces, so that there was hardly a spot left bare. Some stayed perfectly still, some moved while Waver watched, and others seemed still but had definitely been pointing in different directions when they'd been drawn.

The outermost set was aligned to the four cardinal directions, Waver knew, and there was at least one aligned to the current positions of the sun and moon. More pointed at various constellations, the four leyline nexuses within Fuyuki, and six small circles had arrows pointing towards the most potent Spirit Origins in the city to track the other Servants (although Assassin's had remained frustratingly blank since being drawn).

Despite how haphazard it could have looked, it instead somehow all came together in a coherent, almost beautiful whole, where each circle empowered, informed, or fed off all those it touched. A scholarly-inclined magus could receive a masterclass in Bounded Fields just by looking at the floor of Waver's bedroom.

If they did that, though, they'd be missing out on the even greater wonders lying around.

A brass generator the size of a toaster hummed on Waver's desk, glowing with soft blue light. It was fuelled by ambient magic, and if planted near a leyline would be able to power an entire house with room to spare. Wires and cables hung off it in every direction, so that it sat at the centre of a spiderweb of machinery.

A separate stand held Caster's gauntlet – delicate blue runes around the base would teleport it to her hand in the unlikely event she was caught without it. A dozen half-assembled projects were strewn across the floor and desk, arrangements of brass and wires and machinery that Waver could only guess the function of. All were covered in that circuitry-like formalcraft that was Caster's trademark, along with innumerable runes.

One of her mechanical birds cocked its head and chirped as they approached, and Caster scratched it under the chin absently. Smaller automatons – Waver couldn't bring himself to call them 'robots', even though that was exactly what they were – scuttled around underfoot, arranging pages of notes or diagrams or sketches according to Caster's mood.

Caster flopped herself down in the desk chair and fanned herself with a hand. Waver sat down on his bed and folded his hands under his chin.

"Okay," he said. "Talk to me, Caster. You've been quiet all day, which means you're planning something."

"Right-o! Gosh, you do know me well..." Caster picked up a blank sheet of paper and twirled a pen in her left hand.

Waver smiled grimly. "Let me start you off. It's about Lancer, isn't it?"

The twirling stopped, and Caster smile fell, before returning almost full force. "It certainly is! Oooh, I had such plans for Berserker, and that big old meanie went and ruined them all. And, now, well, everything's rather pointless unless we can figure out a way to stop an ancient superweapon."

"I'm assuming you have some ideas?"

Caster laughed, for real this time. "Silly Master, who do you think I am? Of course I have ideas. Whether they'll work is another question entirely, and whether Lancer will politely stand still and let us try them out is another again. But… yes, I think I have an plan for how I'll go about this. However!" Her eyes twinkled with mischief. "What do you think, my student? You've had a day to chew on the problem, so give me what you've got."

Waver sighed. On one level, he was ecstatic that the Servant of the Spell had decided to take him on as a pupil. El-Melloi was a masterful magus and an inspiration even if he was somewhat… abrasive, but Leonardo da Vinci was on a whole other level. And, more to the point, she understood where Waver was coming from entirely. It was incredible, having your ethos of hard work and talent achieving results over mere bloodline validated by an honest-to-goodness Heroic Spirit.

But it did mean that Caster demanded a lot of her Master. Waver hadn't known the Grail War would involve quite so much homework.

"Okay," he started. "So, clearly just hitting Lancer with more and more force isn't going to cut it. They're tough enough to survive a leyline-powered Berserker going all out, can respond with even more force than that, and even when we did manage to hurt them by using a Command Spell, apparently they can just regenerate whatever damage we do. Going by the 'clay man' myth, they might need to be connected to the ground to do that, but that's not exactly much of a limitation.

"If we're going to do this, we need to either deal massive enough damage fast enough that we destroy their Spirit Core before they get in contact with the ground, or else just bypass the problem altogether somehow." He looked up at Caster, to see how he was doing. She smiled, and gave a 'carry on' gesture with her pen.

"So, leaving aside the second option for now… it wouldn't be too difficult to get them into the air, in theory. Not sure how heavy they are, so wind magic or telekinesis might not be the perfect tool, but your portals should do the job pretty easily. We'd need to keep them from falling, so maybe two portals on top of each other, layered so they fell in an endless loop… and probably a forcefield to stop them from just making a chain all the way to the ground and pulling themselves down. Actually," he frowned, as something occurred, "didn't they arrive by flying? That makes this trickier…"

He got up, and started pacing. Machines moved themselves out of his path as he did. "In that case, maybe a sphere of portals, each leading to the other side, leaving no escape. That cuts off Lancer from the ground – and then all you have to do is gather enough power from the leylines to hit them hard enough that their Spirit Core shatters." He stopped. "I feel like it can't be that easy. What have I missed?"

Caster hummed, and waved a hand. "Four things."

"Four?" Waver sighed. He'd thought that was pretty logical, but Caster wasn't ever wrong. He settled back down on the bed and prepared for the lecture.

"Mm-hm! Okay, first, I know I make it look easy, but portals aren't that easy to just fling up willy-nilly. A simple entry and exit point is all well and good, but closing off a space like that? A lot harder. You need at least three sets if you want to make a cube, and the power requirements almost cube as well when you factor in the adjustments to keep spacetime stable as well as maintain all three. Not to mention the mental complexity to keep it all straight in your head. At that point you're better off building something to handle most of the work for you. Not an issue for us, but it is a pretty obvious weak point, and Lancer isn't stupid.

"Second, take whatever estimate you had for how much force it'll take to break Lancer's Spirit Core, and multiply it by, like, a hundred. You might not have seen exactly what it was Lancer was doing to poor Berserker, but your Clairvoyance should be able to tell you – they don't have fixed stats like normal Servants would. In a pinch, they'll direct all resources to withstanding attacks, so we're looking at an effective Endurance of at least A. And, worse, they should have some mechanism for Magic Resistance as well, so we'll have to break through that before even starting to cause damage. Again, not too much of an issue, but that's even more power we'll have to gather beforehand.

"Third… just who were you expecting was going to have to do the dirty work of hitting Lancer with our mega-ultra-super attack, huh, mister? Me, that's who! You want me to step into an enclosed space with the Chain of Heaven? That's a recipe for a very sore head in the morning, let me tell you. Lancer isn't going to stand still and let us hit him – as well as maintaining containment, as well as preparing our alpha strike, and as well as flying because we're doing this in mid-air, remember, I also have to protect myself from an Age of Gods superweapon? Master, that's, like… really, really hard!" Caster looked at him tremulously, fists under her chin, the picture of plucky but overworked innocence.

Sometimes Waver wished he'd just summoned some warrior. Someone big and simple and easy to work with. Sure, he wouldn't be receiving lessons from a world-class genius, but at least he wouldn't have to deal with Caster's whimsical playacting.

He managed to keep a straight face, somehow. "And the fourth thing?"

"Oh, yes. Well, even in the case that we did manage all that, Lancer's Master isn't just going to leave him there. That's pretty much the exact situation Command Spells were built for."

Waver put a hand to his head. "Damn. I can't believe I forgot about those. I was just focused on beating Lancer, and didn't even think…"

"It's an easy mistake to make," said Caster kindly. "That's also the reason we can't just trap him somewhere, or send him into space. We'd get one shot, have to get it right first time or be crushed, and then they'd just reset and be on their guard for things like that."

Well, he hadn't really expected to come up with a solution to the problem in ten minutes of brainstorming. It was still a good lesson, though: even the littlest things could absolutely ruin a grand plan. Kotomine Kirei was formidable, by all accounts, but insignificant next to the power of Enkidu – and yet, his presence was the difference between the plan being 'impractical' and 'impossible'.

"Fair enough," he said. "So how would you-"

There was a knock at the door. He didn't have to worry about his 'grandparents' hearing anything – Caster's spells muffled outgoing noise so that all that could be heard was indistinct voices.

(Absolute silence might have been suspicious, but Caster thought of everything. Waver was pretty sure that a determined listener would be able to make out an actual lesson being conducted, if they tried hard enough – not just the same lesson every day, but an actual syllabus, with accurate information appropriate to Waver's level of schooling, just on the off-chance they were under observation. Caster. Thought. Of. Everything.)

But Waver recognised Martha's footsteps, so he pulled a half-filled exercise book out from under his pillow before making for the door. Caster waved a hand, and the formalcraft circles faded from sight as the machines scuttled under the bed.

Waver counted to two, then opened the door. "Hi, granny."

"Hello, Waver." Martha smiled warmly and lifted the tray held in her hands. "I brought toast? And tea?"

"Oh, granny, you didn't have to…"

"Of course I did, young man! You need feeding up, you'll waste away otherwise. Your father grew up tall and strong – I knew you should have drunk more milk when you were younger…"

Waver studiously ignored Caster failing to hold in her giggles behind him, and plastered a smile on his face. "Thanks… very kind of you…" he gritted out. His 'grandmother' wandered over to the desk and put the tray down before Waver could take it from her hands.

She looked around the room at all Caster's notes and drawings. "This room is so untidy, Waver… it's lovely to have you stay, but mind you clean up after yourself!"

"Will do, granny. Thanks for the toast, we'll take the plates down when we're done, gotta get back to studying, thank you, bye!"

After firmly chivvying Martha out of the room, Waver closed the door and leaned against it. "Sheesh. I know she only does it because she cares, but honestly…"

"Waver."

The hard edge in his Servant's voice made Waver snap his head round. Caster's voice was all business, no playfulness at all.

"What is it?"

In response, Caster put on her gauntlet, and carefully withdrew a note from under the plate of toast. "This. I don't recognise the handwriting, but it isn't either of the Mackenzies'."

She carefully unfolded the paper, taking care to only touch it with her gauntlet. Waver leaned over the desk and read.

His blood turned to ice.

Dimly, he was aware of his heart thumping in his chest – stupid thing, there was no use filling him with adrenaline now. Partly, he felt… violated, angry, strangely indignant. This was his safe space, a place to go to retreat from the perils of the War. That illusion of safety had been definitively shattered. Mostly, he just felt terrified.

"They were here?"

Caster nodded grimly, spell after spell flying from her off hand. They lit up the circles on the floor, which span crazily, function after function activating.

"Are we safe?"

"Clearly not," snapped Caster, before her face softened. "But… I don't think we're in immediate danger. There's a lot more they could have done, and they didn't have to leave a warning like this. I think this is legitimate."

Waver stared at the note, which may as well have been a death threat for all its implied menace.

To Waver Mackenzie aka Waver Velvet aka the Master of Caster,

The Master of Assassin requests a parley to discuss solutions to Lancer.

The toast is not poisoned.

Yours,

Assassin