The saga of the Mennyms has now reached its third volume, and the unusual quality of the series is becoming steadily clearer. For young children of eight or nine this is a comic fantasy about a family of life-size rag dolls, whose secret and embattled domesticity endures the constant fear of discovery by humans.

The dolls were made by a gifted seamstress, one Kate Penshaw, and at her death they came alive to take over her house and build a plausible family life. The fun lies in the game of “let’s pretend” and in the comedy of like and unlike: Mennyms do not eat or drink or feel pain, and supposedly do not die. The adventure lies in threats of exposure, often rashly self-induced. Child readers are admitted to enticing secret lives.

“A good book for children”, goes the saying, “is a good book for anybody”, and the Mennyms stories support it. For older readers the Mennyms’ life is not unlike our own. Like most human beings the Mennyms are perpetually insecure. Elaborate pretences shelter them from awkward truths, or tease life into comfortable shapes. They are playing out a quiet long-term tragedy made bearable by routines, work and risky pleasures. Kate Penshaw is a miniature God, not only their creator but the ghost who in two books now has reappeared to save them. But Mennyms have free will, and not even the providential, loving Kate can rescue them from everything they do.

Mennyms Under Siege is the most serious and best of the books to date. The storytelling is nonchalant and episodic as before. For Sylvia Waugh, it seems, most actions and events are the stuff of comedy even when alarming, and all lives feature plenty of alarms, though often false ones. But sometimes comedy falters, games go wrong, alarms prove true. Mennyms Under Siege contains the worst alarm of all. Can Mennyms die? Yes, it seems they can. Even that they share with people.

By confronting loss and bereavement, Sylvia Waugh subjects her invented world to its severest possible test. Unlike her characters, she is not a great one for “pretends”. From the start of her first book, with its epigraph from Housman (“I, a stranger and afraid In a world I never made”) the Mennyms stories have prepared for such a moment, and when it comes the author’s sensitivity is equal to the task. It is a remarkable achievement.