Pulse (A Kate Redman Mystery: Book 10) - The Kate Redman Mysteries, #10

The body of a young man is found in a graveyard the night after a wild, drug-fuelled party. At first glance, there doesn't appear to be anything sinister about his death, despite the shock of Detective Inspector Mark Olbeck realising that he once knew him. Detective Sergeant Kate Redman has other things to worry about, not least her ongoing affair with her superior officer Chief Inspector Anderton.
But when a second body is found in suspiciously similar circumstances, Kate, Olbeck and the rest of the Abbeyford police team realise they are up against a devious killer who will stop at nothing to indulge a literal thirst for blood.