Some few weeks after their adventure with the stampeding horse in London, Thomas Lynn calls to invite Polly Whittacker to visit him again, as he has something to show her. It turns out to be a small, teapot-shaped cream-yellow car with the number plate TC 123. Polly exclaims at this, "a modern horse! And TC for Tan Coul!"
And Tom agrees that as soon as he saw the number plate, he knew he had to have it. They go driving off in the country, because Tom has discovered that there really is a place called "Stow-on-the-Water" and they are going to drive to it in the horse-car. Which they do, and many strange coincidences begin to emerge there.