When their father Augustus Callendar, a famous newspaper correspondent, is called away from home to cover an international crisis, February and her brother Friday escape their tutor and uncover an international crisis of their own! While the United States and Russia maneuver to seize an unbelievably explosive mineral newly discovered on the small island of Capria, February and Friday search frantically for clues that might unravel the mystery, expose the villain and, hopefully, save England. The action is fast-paced, spine-tingling and riotous as our intrepid duo follow a trail that leads them right back to where it all began - to Friday's tunnel - in the Callendar back yard.

Augustus Callendar, newspaper columnist and father of the zany Callendar family, has campaigned for years for the construction of modern roads in Britain, and he is delighted when the Ministry of Highways finally takes up the suggestion—until he learns that the first new highway will run right through the Callendar farm! February, the oldest daughter and chronicler of family events, is most unhappy at the prospect of losing the fields where she rides her horse, Gorse; and besides, she suspects that shady dealings have taken place. She snoops around and naturally lands all the Callendars in a mess.

What is this mysterious new movement, ismo, spreading across the world? Is it a force for good or evil - or both? Whatever it is, ismo in action plunges February, Friday and Gail Callendar and their father into the most fantastic and wildly funny adventure ever recorded, involving a trip from London to France, an art theft, and a plot to murder President de Gaulle!

The Callendar family undertakes research to disclose why a breakfast mix has such a fantastic effect on race horses.

The Callendar family has moved from Marsh Manor to the center of Querbury. Gus Callendar is standing as an Independent candidate in the forthcoming local elections. The Council has plans to pull down a spendid disused maltings in the center of town to make way for a new road. But Gus and his followers want to turn the maltings into a community center from which the whole town would benefit. It is young Berry Callendar who is finally the focus of her own story in this active family's chronicles.