Stacey and the Mystery at the Empty House

Stacey and the Mystery at the Empty House is one of the Baby-Sitters Club mysteries by Ann M. Martin, published in 1994 and written for younger readers who like a puzzle alongside their babysitting.

Charlotte and her family set off for France and leave Stacey in charge of the house and the dog, which sounds like easy work for somebody with her experience. Within the first couple of days she begins to notice things that do not add up. Carrot growls at nothing, glasses of water appear that she did not pour for herself, and one of the hairbrushes contains orange hair that belongs to nobody in the household. Stacey has to work out whether somebody has been inside the house without permission, and whether they are still there, while keeping the situation from becoming a panic for the children she is responsible for.

Martin's mystery series sets its teenage members in ordinary houses and lets the puzzle grow out of small domestic details, which is why the evidence in this one amounts to a glass of water and a hairbrush.