Thousands of people are set to line the capital's streets to watch Paralympic hero David Weir go for a quadruple gold crown in the T54 wheelchair marathon.
The Londoner is unbeaten in this year's Games, winning all three wheelchair races in which he has competed and earning a place in the nation's hearts while doing so.
The 33-year-old, whose trademark "Weirwolf" howl has become one of the sounds of the Games, will speed past some of the world's most recognisable landmarks in the race.
He lines up alongside his long-time rival, Switzerland's Marcel Hug, for the start of the 26.2 mile looped course with the opportunity to take his fourth gold of this Paralympics, and sixth in his Games history.
Competing in the women's race is Shelly Woods, who will set off shortly after the men's race at 11.30am. The 26-year-old will be looking to improve on her sixth-placed finish in the T54 1,500m - having gone into the competition as the reigning silver medallist.
Organisers have confirmed the event will not be broadcast live on television, meaning thousands of supporters are expected to line the streets for the course instead.
The route is different to that of the traditional London Marathon, featuring one 2.2-mile and four eight-mile laps, taking in sights such as St Paul's Cathedral, Buckingham Palace and the Houses of Parliament.
Weir said: "The course is very twisty. It's not going to be banging out top speeds for a long while so hopefully I can get the endurance and get through it. We'll see."
Those who venture to the streets to watch the marathons can expect warm weather, as Britain's Indian Summer continues. Billy Payne, forecaster with MeteoGroup - the weather division of the Press Association, said that central and southern areas of England will have another "very warm day", with temperatures reaching 27C or 28C (82.F).
Jackie Brock-Doyle, Locog's director of communications, said Channel 4 would show the start and finish and provide regular updates from the marathon. "It is part of the decision Locog took with OBS (Olympic Broadcasting Service) and the other broadcasters for what we could do with the broadcast money raised," she said.