The Whispering Skull is a book by Jonathan Stroud, who wrote the excellent and fun Bartimaeus Trilogy. Published in 2014, this is the second of series called Lockwood & Co., following The Screaming Staircase, set in an alternate history of England in which ghosts and other spectres have turned out to manifest themselves. As young people are more susceptible to hauntings, they are trained to hunt down and capture or destroy these 'Problems'.
As with many sequels in a series, the world built in the first is expanded on in teasing bits. We learn of religious sects foolishly desiring to contact The Other Side by welcoming in ghosts to their meetings (and often coming to sticky ends). Of people in power desiring much more power by harnessing control of spirits through haunted and possessed objects. Of a black market of gravediggers, relic sellers and their sinister buyers.
The skull of the title made an brief apparitional appearance in the first book, and comparisons can be made to Bartimaeus' personality in Stroud's most famous series, especially in aspects of sulkiness and deceit. Our trio from the previous book have survived and are building up a good reputation for dealing with 'Problems'. Although their own triangle of personalities continue to clash and quarrel --goaded by the whispering skull--, when they band together their talents are able to get them through some terrifying torments by the skin of their teeth. Along with a truly scary haunted house, there are battles in catacombs and --again familiar to readers of the Bartimaeus Trilogy-- warehouses.
A particularly interesting detail is the narrator often mentioning the quite decent daytime weather in London. Something isn't right here, but it won't be addressed in this book.
Filled with true dread and explosive action, the premise set up from the previous book continues to reward with scary encounters, especially in the haunted house section.