Eddie Izzard is in the British Olympic medical centre, telling a doctor he plans to run a marathon a day, six days a week, for seven weeks -- a round trip of 1,166 miles through England, Wales, Scotland and Northern Ireland in aid of Sport Relief.
"I've run before," Eddie tells him, "but mainly for buses." Ha-ha! This is Eddie Izzard, after all, brilliant stand-up comedian, accomplished actor and also a transvestite more used to treading the boards in high heels than pounding the roads in trainers.
No, but seriously, what running has he done? "When I was a kid I ran around a bit in the playground. I think I was built for running," says Eddie, who looks like he was built for lying on a sofa.
Ha-ha! And how long has he been training?
Three weeks. A professional athlete would normally take nine months to prepare for a feat like this, so how long has Eddie got? Five weeks. The doctor puts down his pen and turns to the camera crew: "Is this for real?"
But it is for real.
Five weeks later, having been whipped by his trainer, Dr Greg Whyte, into the best possible shape a tubbyish, 47-year-old man with no running experience can be, Eddie sets off from Trafalgar Square for his first 26.2-mile stretch, English flag in hand, accompanied by the camera crew and the medical team, travelling in an ice-cream van and a battery-powered rickshaw.
Eddie's running technique is as digressive as his comedy act. He stops off to sightsee, nips into a shop to buy a Calippo and admires some ducks.
Nine miles in, his stop-start routine catches up with him as old injuries begin to flare up. But he makes it to the end, slowly, in 10 gruelling hours.
By the end of the second day, his legs are already seizing up and there are blisters on his feet. The medic lances them, gives him painkilling injections and fits orthopaedic inner soles to his trainers to compensate for his flat feet.
He looks mentally and physically exhausted by the third day.
This is no vanity-driven celebrity star trek. Eddie's in agony all the time. The blisters become infected and he strips a long tendon in his right leg.
His manager, though, knows he will carry on. "He has no fear," she says. "He's walked the New York subway in six-inch heels."
Eddie perks up when he's joined for a few miles by a 72-year-old athlete who ran across America in 64 days straight.
Everyone, this man says, runs to prove something to themselves. For Eddie, charity aside, the goal on this first leg seems to be to reach the house in Wales he shared with his mother, who died when he was six.
When he does, it's a moving moment, full of happy and sad memories.
It seems to regenerate him, driving him on through the Brecon Beacons, a punishing series of steep hills. Episode one leaves him nine marathons in, his brain and body at last beginning to click together.
There's a lot of running ahead, but this is a terrific piece of television, funny, touching and genuinely inspiring, and worth every painful step. Go, Eddie!
TOMORROW: Pat headbangs along to Heavy Metal Britannia (BBC4)
Eddie Izzard: Marathon Man *****