The Screaming Staircase by Jonathan Stroud

For more than fifty years, the country has been affected by a horrifying epidemic of ghosts. A number of Psychic Investigations Agencies have sprung up to destroy the dangerous apparitions.

Lucy Carlyle, a talented young agent, arrives in London hoping for a notable career. Instead she finds herself joining the smallest, most ramshackle agency in the city, run by the charismatic Anthony Lockwood. When one of their cases goes horribly wrong, Lockwood & Co. have one last chance of redemption. Unfortunately this involves spending the night in one of the most haunted houses in England, and trying to escape alive.