Professor Slughorn knew that something was seriously wrong once Lily Evans skipped a class.
Noting his favourite pupil's absence from her seat beside the slightly less (but still ever so) prodigious Severus Snape, Slughorn tutted to himself as the last stragglers of the fifth-year class trickled into the classroom, their eyes flashing at the pre-prepared brews bubbling in the cauldrons on his desk. What was even more strange was that this was a revision lesson smack bang in the middle of O. - the Potions examination was near the end, and so Slughorn had scheduled several classes to refine his pupils' techniques. As gifted as Lily was, the Professor knew that she'd rather bite off her own leg than miss this class.
However, he couldn't dwell on this. He had a class to teach.
"Snape, my boy, will Miss Evans be joining us?" He asked briskly, turning on his heel and walking casually over to his desk towards a vial of pale blue potion placed neatly on the worktop. The general classroom chatter died instantly, the air turning deathly still - Slughorn had stepped into something big, apparently. Now, that was certainly odd - he usually prided himself on knowing all the fruit of Hogwarts' grapevine.
When Snape did not respond, Slughorn turned to face the class, vial in hand, frowning slightly as he sought out the thin boy's face. He noticed that the usual sallow skin was now flushed with - what, exactly? Embarassment? Shame? Severus' head dipped downwards, his face turned towards the smooth wood of his desk, mumbling something unintelligbly.
"Sorry, Severus, I didn't quite catch that."
"I said I don't know, Sir."
The chill in the air was perceptible even to Slughorn's tactless self. He noticed several students clad in scarlet and gold ties glaring at Snape murderously. Even Potter and Black, usually boisterous and cheeky, had stopped their shenanigans to direct deathly glares in the Slytherin's direction.
Slughorn cleared his throat.
"Very well, um… Miss McKinnon?" The blonde, sitting at the desk beside Snape's on Lily's side, responded in a snipped tone, her eyes never leaving the boy's bowed head.
"She's not feeling very well, Sir. She's visited Madame Pomfrey, though. Hopefully she'll be back next lesson."
Slughorn, not wanting to make the atmosphere any frostier, hurriedly started the lesson, explaining the contents of each cauldron and the proper techniques to brew them in a forcibly cheerful tone.
Severus didn't take any notes.
—-
Lily Evans did indeed return to the next lesson, scheduled three days after the first. She seemed her perfectly normal, vibrant self; her hair freshly washed, her blouse free of creases and tucked neatly into her skirt. Slughorn eagerly awaited her arrival without making it obvious - as she entered the room, surrounded by her friends as usual, the Professor beamed and nodded once in her direction, receiving a small smile in return. He noticed that her fellow Gryffindor girls, especially Miss McKinnon and Miss MacDonald, were clinging even closer to her side than usual, almost protectively. It was only when he looked closely at the Prefect that he noticed the red splotches fading away from her pale face, her eyes ringed with a slightly darker shade that only came with a lack of sleep, her particularly bright green eyes darting to her usual seat worryingly. As other students slouched into their places, she approached Slughorn quietly.
"Sir?" She asked in a hushed tone, a wall of depression and fragility clearly present in her expression, "Sir, would it be possible for me to switch places with Marlene? Please?"
How could Slughorn say no? Even if she hadn't been his favourite pupil, he would never have had the heart to deny the pitiful expression on her face. He suddenly felt a paternal urge to curse whatever had stricken her so, before beating down the impulse and smiling reassuringly at her.
"Of course, Lily." He responded in an equally quiet voice. Lily nodded and walked over to Marlene, who had been hovering by her desk; immediately, the blonde smiled weakly at her friend, before strutting over to Lily's usual place beside Snape, not looking once at him. The boy winced as Marlene slammed her satchel down onto the wood, shaking the stand on which his cauldron sat; Lily's eyes flickered over to the pair, glazing over with what looked suspiciously like tears - she blinked them away, but Slughorn noticed.
Everyone else had settled down as Marlene unpacked. Mary was mumbling encouragingly in Lily's ear, the redhead nodding determinedly, though still looking as if she would shatter at any given moment. Marlene's final item smacked into her desk with such a violent crash that Peter Pettigrew, sitting near the back with the other Marauders, flinched at the sound.
Throughout the entire lesson, Lily never once looked at Snape, who either begged her with his eyes to notice him, or stared down into his textbook once his new desk-mate caught him in the act. As a Professor, it was incredibly awkward to try and push through the obvious tension in the room, and it didn't help that Potter was glaring furiously at Snape's head of greasy black hair, his own resting on his folded arms, tapping his wand against his elbow impatiently, as if he couldn't wait to jinx the Slytherin.
That was exactly what he did - or at least, that's what Slughorn thought. He'd never found any evidence to prove it, but when he found Snape sprouting elephant tusks outside his classroom, he had been sure it was Potter's handiwork, despite the fact that both Potter and Black had disappeared into thin air.
—-
Slughorn was surprised that he'd had such a turnout for N.E.W.T Potions; almost everyone had achieved an E, even Peter Pettigrew, who Slughorn suspected had squeezed many hours of tuition out of Remus Lupin to reduce the amount of times he'd set his cauldron accidentally on fire.
To his delight, Lily Evans strode into the classroom gracefully, happy once more - but, of course, he already knew that she'd perked up. He and Lily had spoken at several of his Slug Club functions after O. - week by week, she'd started to gradually become herself again, until by the time the Hogwarts Express brought the students to school from King's Cross for another fresh new year, she bounced with the same spring in her step as she had had before. Surprisingly, she took her seat beside Severus, whilst Marlene returned back to Mary. Severus looked astonished, but Lily did not look at him; she took out her brand new Potions textbook from Flourish and Blott's and kept her eyes trained on the Professor, her green eyes boring into him. He coughed awkwardly as the class filled up. He'd used up all of the usual small talk at the welcoming feast two days before, and finally managed to dredge up a topic of conversation.
"Ready for the first Potions lesson, Lily?"
"Of course, Sir. I actually read up on the properties of scurvy grass for that lesson you mentioned, it's really interesting, especially the part about combining it with bulbadox juice…"
"Ah, wonderful! You never fail me, Miss Evans."
She flashed a brilliant smile at him and he proceeded with the lesson. Once he had set the class to work on their very first N.E.W.T level potion, he began to stride between aisles, offering tips as he went.
"Black, Merlin's beard boy, don't be so reckless! Add the shredded wormwood gradually. Pettigrew, you stir twice clockwise, not anticlockwise - you'll have to start again, it'll just start smoking and popping in a minute. Very good, Lupin, excellent, Avery…"
He worked his way up towards the front of the class, and was inspecting Marlene's violet potion when he heard a snatch of conversation behind him.
"Snape, your dittany's on my belladonna… Thanks."
"Lily -"
"I'm sorry, do you have something to say to me?"
"Lily, please -"
"You know what, I don't want to hear it. Save your words talking to someone who's worth it, if you get my drift?"
Severus didn't respond. Slughorn felt a shiver down his back as he thought of the broken bond between his two favourite pupils. What could possibly have wrought this much damage between a pair who had been best friends since childhood?
He proceeded to comment on their potions.
"Lily, perfect as usual, ten points to Gryffindor! Oh my, Snape, what's happened? You're not usually this careless! Add some foxglove to get it back to the lilac colour, and continue from step four." It was difficult to keep up the ignorant, normal-teacher facade, but Slughorn managed it, striding back to his desk and sitting down to look up his schedule for the rest of the week. How Snape could go from being a master at Potions to producing that awful standard of brew, he had no idea.
At some point early on in sixth year, Lily, Marlene and Mary managed to secure one of the three-person desks in the middle of the classroom, directly in front of the Marauders, and stayed there for the rest of the year. Severus worked alone.
