A heatwave hits the network hard, with signalling equipment out at Didcot, rails in need of stretching in London, and a surfeit of insects overworking trains' windscreen wipers.

A nasty surprise awaits engineers as they discover rotten wooden sleepers that disintegrate under foot. Even veteran train staff are shocked by the reason the 15:00 to Bristol has come to a halt - a driver tried to start the train from the wrong end.