"And this is the stationery cupboard." The Brigadier held the door open while the auditor, Mr. Dorsley, peered in over the top of his tiny spectacles.

"I see," said the smaller man, marking a squiggle on his clipboard. "And what do you keep in here?"

The tip of the Brigadier's moustache twitched, ever so slightly. "Stationery, primarily. Pens, pencils, staplers -"

"Yes, I know what stationery is, Brigadier. I'm not an imbecile," Dorsley tutted. "And what is your annual expenditure in this department?"

"Three hundred and seven pounds, fifteen pence last financial year," he replied instantly, having memorised this and other important figures purely to deny Dorsley the small victory of stumping him.

"Oh… well that… doesn't seem like a proper amount," he managed as the Brigadier closed the cupboard door.

"And what would be? A proper amount, that is?"

Dorsley smiled infuriatingly. "Less, Brigadier! Less!" The auditor turned his head suddenly. "I say! What is that dreadful noise?"

The Brigadier's heart sank. The harsh, steady roar of a blowtorch was coming from the laboratory at the end of the corridor. "Ah, that would be our scientific advisor. Eccentric chap - he insists on supplying all his own equipment and materials, so there's really no need for you to…"

But Dorsley was already marching towards the open doorway. Clearly, the concept of something not being his business was foreign to the man. The Brigadier braced himself and followed the auditor in.

All the usual clutter of the Doctor's workspace - the disassembled electronics, the flasks and beakers and bunsen burners, even the coat rack and workbench - had been pushed up against the walls and around the badly parked TARDIS. The remaining floor space was now taken up by an enormous tetrahedron, constructed from six intricately etched metal girders. At the moment the two men entered, the Doctor was kneeling by one of the lower vertices of the structure with his back to the door, adding the finishing touches to a weld.

"Good heavens, man!" spluttered Dorsley. "What in heaven's name - where is your safety equipment?"

"No need," said the Doctor, still with his back to them. "Special torch of my own design. Invisible flame, no sparks." He held the nozzle up and gave two quick bursts to demonstrate.

The Brigadier watched Dorsley take this in. "And who owns the patent on this device?" the auditor asked.

The Doctor finished his weld and stood up. "We haven't been introduced," he said, turning around. "I'm the Doctor. And you must be from the government."

Dorsley's reply was cut off by the opening of the laboratory's outer door.

"Doctor, Lom is amazing!" gushed Jo Grant as she stepped inside. "I was showing her the woods nearby, and do you know she can tell the age of a tree just by - oh!" Jo stopped short as she caught sight of the the room's other occupants. Sergeant Benton followed her in and stood to attention. Lom the Intersector trailed in serenely after him, staring off into the middle distance with the slightest of smiles on her silver face.

Just marvellous, thought the Brigadier, taking in the crowded tableau. "Well, I believe introductions are in order," he said finally.

Dorsley remained silent during the exchange of credentials, though he was not visibly shaken by the sight of Lom. "Yes, yes," he snapped, cutting off the Brigadier's explanation of their visitor. "I have been briefed on the nature of UNIT's activities. Though I can't say that I approve. My primary concern is the expenditure of government resources on this… folly." He flapped his hand at the tetrahedron.

The Doctor glowered. "This "folly" is a full-spectrum exotic particle manifold scoop. Its true function will escape the grasp of even the best scientists your planet will produce for at least a century. You'll forgive me if I don't bother trying to explain it to you." He spoke more gently to the Intersector. "I hope this meets your requirements, Lom."

Lom gently stroked the apex of the tetrahedron. The metal sang under her touch, a pure, unearthly note. "It is well. The harvest begins near."

"Here? On Earth?" The Doctor furrowed his brow. "But there's nowhere…"

"Soon." Lom gestured towards the tetrahedron - the scoop - and it lifted into the air as if on wires. As the Intersector turned and walked purposefully through the outer door, the device rotated slowly after her, passing straight through the surrounding wall with no more resistance than one shadow crossing another.

Jo crept in close to the Doctor as she watched Dorsley's reaction to all this. "I don't like the look on his face," she whispered.

"Nor do I, Jo," the Doctor agreed. Dorsley's expression had turned so obviously avaricious it was practically green.

"Such power!" the auditor marvelled. "If she could just be convinced to put it to use for my - that is, for the government's purposes…" Dorsley abandoned his clipboard on the bench and rapidly buttoned his coat. "The audit has been suspended, Brigadier. Higher priorities, national security, that sort of thing. Above all your pay grades." He paused on the way out and stabbed a finger towards the TARDIS. "But I shall insist on conducting a full inspection of the contents of that cupboard when I return."

"Then you'd better bring a pack lunch," said Jo as the door closed behind him, causing Sergeant Benton to stifle a laugh.

"Well, Doctor?" asked the Brigadier.

"The harvest." He stroked his chin. "It's a sort of ritual that each Intersector has to undertake once in their life. They must find and absorb a massive dose of exotic particles - tachyons, mostly - and thereby stabilise their own existence as a metadimensional being."

"Like a cross between a pilgrimage and a vitamin shot?" offered Benton.

"That's one way of putting it, sergeant. I constructed the manifold scoop to assist Lom with her own harvest - but I didn't imagine she'd be performing it here. The TARDIS is too well shielded to be of any use to her, and there's no terrestrial technology in this era that would be suitable."

"What about the Breakridge Institute?" said Jo. "They're doing research into zero-point energy. It's very high-powered stuff, too."

Jo was suddenly aware that she had become the centre of attention in the room. "What?" she countered. "A girl can't read New Scientist?"

The Doctor beamed. "Jo Grant, I think you've cracked it! Breakridge is only a few miles north-east of here as the crow flies."

Benton peered out the window. "Looks like north-east is the direction Lom is headed, Doctor. Mr. Dorsley too."

The Brigadier frowned. "That man. Could he become dangerous, Doctor?"

"He won't turn Lom against humanity, if that's what you mean Brigadier. But he might confuse her into doing something harmful."

"Why don't I go after them?" said Jo. "I can make sure they stay out of trouble. Besides, I've always wanted to be a shoulder angel!"

"Good idea, Ms. Grant," said the Brigadier. "Take Sergeant Benton with you, in case Mr. Dorsley forgets his manners. And you and I, Doctor, had better get over to this Breakridge Institute. We can't have any more civilians getting caught up in all this."

"My thoughts exactly." The Doctor picked up his coat, adding as Jo and Sgt. Benton headed out, "Though I'm afraid the TARDIS has been in a bit of a mood lately. We'd better take Bessie instead."

"Oh good," said the Brigadier. "Much more reliable."