"Right. I'm on a railway platform waiting for an overdue train. It's about two hundred degrees in the shade, the pigeons are falling out of the sky from heatstroke, and nobody will sell me a beer." (Well, they might if I'd asked for one, but . . .)

"Oh, good! When are you going to be back?"

"Sometime late this evening," I say doubtfully. "I'm due to arrive in Cosford at"—I check the lying timetable—"two thirty, and I don't think I'll get away before six. Then it'll take me about three hours—"

"Angleton did this? He did, didn't he!" Suddenly Mo switches from warm and cuddly to spiky as a porcupine: "Didn't you tell him you couldn't? We're supposed to be having dinner with Pete and Sandy tonight!"

I do a mental backflip, re-engage my short-term memory, and realize she's right. Dinner for four, booked at a new Kurdish restaurant in Fulham. Pete was at university with Mo years ago, and is a priest or a witch doctor or something; Sandy is blonde and teaches comparative religion to secondary school kids. Mo insists we stay in touch with them: having friends with ordinary jobs who don't know anything about the Laundry provides a normative dose of sanity for the two of us, to keep us from drifting too far out of the mainstream. "Shit." I'm more mortified for having landed Mo in it than anything else . . . "You're right. Listen, do you want to go on your own, tell them I'll turn up later—I'll come straight from the station—or do you want to cancel?"

There's silence for a second, then she sighs. "Sandy doesn't have flexitime, Bob, she's got classes to teach. You cancel."

"But I don't have their mobile numbers—"

I'm bluffing, and Mo knows it. "I'll text them to you, Bob. Maybe it'll help you remember, next time?"

Bollocks. She's right: it's my fault. "Okay." It's my turn to sigh. "I'll be claiming some hours back. Maybe we can use them for something together—" The tracks begin to vibrate and squeal and I look up. "It's my train! See you later? Bye . . ."

The train to Cosford is about as old as Angleton: slam doors, wooden partitions, and high-backed seats, powered by a villainously rusted diesel engine slung under its single carriage. Air conditioning is provided by the open louvered windows. I swelter in its oven-like interior for about forty minutes as it rattles and burbles through the countryside, spewing blue smoke and engine oil behind it. Along the way I furtively leave my apologies on Pete and Sandy's voice mail. Finally, the train wheezes asthmatically to a halt beside a station overlooking a Royal Air Force base, with a cluster of hangars outside the gate and some enormous airliners and transport aircraft gently gathering moss on the lawn outside. Breathing a sigh of relief, I walk up the path to the museum annex and head for the main exhibit hall.

It's time to go to work . . .