Tabitha Plimtock lives in a house at the very edge of the world. She is a go-getter - that is, a dogsbody forced to go and get things - for her nasty relatives, Gower, Gristle, Bertha and Cousin Wilbur. One of Tabitha's endless chores involves descending the cliff face, via a net that hangs from the back of the house, to collect eggs, nuts and other things from the inhabitants of the wall. When rumours begin to circulate of monsters climbing from the base to gobble up unsuspecting wall-dwellers, Tabitha is worried for all her friends. Determined to save them, Tabitha seeks out the elusive and eccentric Dr Sherback. The doctor introduces her to a whole new world at the base - one that is dark, dangerous and absolutely thrilling - but not even Dr Sherback's vast knowledge can slow the terrible creatures climbing to the top of the wall. With a clever plan, and not a small amount of courage, can Tabitha stop the monsters and keeps the people she loves safe for good?