The Women of the WISE Enquiries Agency are back. Henry Devereaux Twyst, eighteenth duke of Chellingworth, is terribly worried about the books in the lower library ...so much so, he invites a local bookseller and antiquarian to examine and restore them. When the man in question mentions to Althea there are some strange shenanigans going on at his shop she's all a-twitter and brings his problem to her colleagues at the WISE Enquiries Agency. The bookseller is baffled by the fact that, despite doing a pretty good job with book sales, he winds up with more books at the end of the month than at the beginning. Carol - ably "assisted" by her infant son Albert - tries to track down the one-time owner of the books, and it's discovered - through solid investigative teamwork - that he and his wife run an old-folks home. This discovery, whilst helpful, leads to a nagging suspicion among the WISE Women that maybe everything isn't as it should be at the home; and Althea relishes the chance to disguise herself and check into the suspicious old-folks' home to do some undercover sleuthing.
The entire team is called upon to act when Althea "goes dark" and isn't heard from for more than twenty-four hours.