In summer 2009 Eddie Izzard attempted the ultimate human endurance challenge for Sport Relief - running a staggering 43 marathons in 51 days around the UK. Covering 1166 brutal miles around the United Kingdom he ran a marathon a day, six days a week, for eight weeks. This is the gripping final episode of the inspiring three-part documentary series following Eddie's epic adventure. He has already run 700 miles, but still has to complete another 462. Setting off from Glasgow he is on a tight schedule to get to the finish line in London on time. He has set himself the herculean task of completing the final 17 marathons in just 19 days. It's a peculiar British odyssey cooked up in Eddie's head, to run the United Kingdom brandishing the flag of each country he runs through and visiting interesting places where he lived or stayed during his life. Eddie's route takes him through Edinburgh, where he meets old friends from his days as a struggling comedian. He is joined and supported by celebrities including Denise Van Outen and Frank Skinner along the way. But once he leaves Edinburgh he's alone once more. He faces isolation and extreme temperatures in the unforgiving Scottish countryside on the way to Newcastle, suffers painful stomach problems caused by an extreme diet, battles through insomnia, and the tortuous daily routine of nightly ice baths becomes unbearable. But Eddie is no longer an unfit comedian. He's running faster, stronger and getting more support than ever before. Visiting Alzheimer's sufferers at a Sport Relief project en route, he is inspired to keep on going, battling through the difficulties and mental barriers. However, by running so many consecutive marathons with little rest it's only a matter time before his body breaks down. With just five marathons left Eddie suffers his worst injury so far. Now he's in a race against time to make it to the finishing line and he's determined to run, walk or crawl to get there.