The book is set in 1960's rural England. Dobbs one of the farm carthorses has been working with farmer Parr clearing a field of stones and other debris. The farmer leaves Dobbs in the field, and goes for a drink of cool lemonade in the hot afternoon summer sun. Dobbs mysteriously disappears down a hole that opens up in the field. Millie the farmers daughter, and the farm animals decide to launch a mission to rescue their friend Dobbs. Difficulties arise when the field is cordoned off by the police because it is a safety hazard. The field was also the site of Roman and Anglo Saxon settlements, which prompts the government archaeology department to get involved.