Kids and shoppers and office workers in suits and shop staff in uniforms move around her; she threads her way between them, not looking in shop windows or diverting her attention from the destination in hand. Here's a side street, and she turns the corner wide—avoiding a baby buggy, its owner nattering on her mobile—and strides along it before turning into another, wider street at a corner where a bland seventies office rises six stories above the pavement.

The office has glass doors and a reception desk fronting an austere atrium; a bank of lifts behind it promises a rapid ascent into crowded beige cubicle heaven. The woman approaches reception, and holds up an ID card of some sort. The guard nods, signs her in, then waves her on to the lift bank on the right. She could be a session musician turning up at one of the TV production companies listed on the wall panel beside the reception desk, or a member of staff on her way back from a lunchtime lesson.

But she's not.

The lift control panel shows five numbered floors. As the door slides closed, the woman pushes the third-floor button, then first floor (twice), then the fourth floor. The lift begins to move. The illuminated floor display tracks it up from ground to first, second, third—and it goes out. Then, safely stranded between indicated floors, the doors open.

There are no cubicles here: only rooms with frosted glass doors that lock shut, and red security lights to warn against intrusion. Some of the rooms are offices, and some of them are laboratories, although the experiments that are conducted in them require little equipment more exotic than desktop computers and hand-wired electronic circuitry.

The red-haired woman makes her way through the building with ease born of familiarity, until she finds room 505. She knocks on the door. "Come in," the occupant calls, his voice muffled somewhat by the wood.

Mo opens the door wide. "Dr. Mike," she says, smiling.

"Mo?" He has a large head for his average-sized torso: brown hair fighting a hard-bitten retreat, bound in a ponytail; his eyebrows, owlishly peaked, rise quizzically at her approach. "Good to see you!"

"It's been too long." She walks in and they embrace briefly. "Are you busy?"

"Not immediately, no." His desk tells a different story, piled high in untidy snowdrifts of paper—there's a laser printer on a table in one corner, and a heavy-duty shredder right below it—with a coffee mug balanced atop one particularly steep pile. The mug reads: DURING OFF HOURS TRAINS STOP HERE. There's a bookcase beside the desk, crammed full of phrase books and travel guides, except for one shelf, which is occupied by a tiny Z-gauge model railway layout. "Were you passing through or can I be of service in some way?"

"I was hoping to talk to you," she confesses. "About . . ." She shrugs. "Mind if I sit down?"