Drain — Scott Richards

Three teenagers, playing on local waste ground during an autumn half-term break, kill a rat.
In the sewers beneath London, an initiation prank, played on a new recruit by a team of "flushers", backfires.
Police investigating the suicide of a patient at a geriatric hospital, find it inexplicably linked to the recent murder of a wealthy young man.
An electrician at the hospital harbours an unhealthy obsession for one of the nurses, which gradually festers, becoming dark desires but, ultimately, murderous rage.
When the lights go out at The Beeches, patients and staff roam deserted corridors, stalked by a killer, and the screaming begins.
Not for the squeamish.