Sir Piers Willoughby, squire of Steyne Winting Manor, is a widower with seven children, but since his wife's death some three or four years before the story begins, he has taken to travelling all over the world and is rarely at home.
His only near relation is his brother Nigel, eighteen years his junior, and so the children are left to the care of the housekeeper at the manor. All of them are educated at home. Maidie, the eldest, has been mistress of the house since her mother's death.
Madelaine (Maidie), Reginald (Rex), Marjolaine, Peter, David, Bernadine (Dina) and Tim are known to their neighbours as "those imps" or "them brats o' squire's", and are rarely out of mischief. One night the children plan an escapade which sets the household in an uproar, and the curate, Mr. Eltringham, decides that someone must take a firm line.
Sir Piers is summoned home and arrives a few weeks later, bringing with him a lady. He introduces her as his new wife, Sigrid - and with her is Britta, her daughter from her first marriage.
Sigrid tries hard to make friends with her stepchildren, but they are slow to respond. Then Dina undergoes a serious operation and is very ill and is sent to Guernsey to convalesce, the entire family accompanying her on Nigel Willoughby's yacht Sea Dweller. In their concern for Dina, the Willoughby children begin to accept their new mother and sister.
On the island they all make new friends, first Janie Temple and Pauline Ozanne, then the Atherton family and Julian Lucy, and later the Ozannes and the Chesters.
The arrival of Mr. Eltringham (the object of intense dislike by all the young Willoughbys) prompts the youngsters to all kinds of mischief. Finally, the rescue of eleven-year-old David from an accident on the cliffs brings the book to a happy conclusion.
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