By Lis Carey: The London Underground has ghosts. Well, the London Underground always has ghosts, but usually they’re gentle, sad creatures. Lately there’s been an outbreak of more aggressive ghosts. Groping, shoving, insults that are racist and/or misogynistic–offensive and provocative. Victims of the assault report them, but have completely forgotten them by the time Transport Police get back to them to follow up.

Jaget, the member of the Transport Police most adept at seeing ghosts, calls in Peter Grant, Patrol Constable and Apprentice Wizard, part of the only unit of the Metropolitan Police that deals with ghosts and other spooky stuff. He in turn brings along Abigail, who, yes, is only a teenager, but as someone, perhaps Nightingale, says, she sees ghosts when she’s on her own. Just as well to have her supervised and learning how a proper investigation is run.

They start by trying to find a pattern, and by trying to interview new targets of the ghosts quickly enough that they get some information before the memory fades. When they encounter some ghosts, a strange thing happens. Or, another strange thing. They can interact with these ghosts, to the extent the ghosts are able to interact, for a few minutes. Then the ghost doesn’t leave, or fade. It shatters. That is not previously documented ghost behavior.

Abigail, having had great success in her Latin studies, is allowed to read books in the Folly’s library that Peter is not yet authorized for. This annoys Peter in two ways. One, she’s very much his junior. Two, he promised Abigail he would teach her Latin if she learned Latin. She’s now better at Latin than he is. Abigail also finds what might be a clue, an account of a house at the end of the Underground line where the strange ghosts have been appearing, where a magician of some kind lived.

Peter, meanwhile, meets a toddler river god living with an older, childless couple. Nothing to see here, look away, look away…

It’s not long before they’re tracking a kidnapped commuter, and learning strange things about the uses of trapped ghosts.

Oh, and Peter and Nightingale are worrying about how they’re going to talk to Abigail’s parents about her need to be trained as a wizard.

It’s a lot of fun. Highly recommended.

I received a free copy of this book, and am reviewing it voluntarily.

• The Furthest Station (Rivers of London #5.5) by Ben Aaronovitch. Subterranean Press, ISBN 9781596068346, June 2017