Bleeding Heart Yard: Elly Griffiths

A propulsive new thriller set in London featuring Detective Harbinder Kaur. A murderer hides in plain sight - in the police.
DS Cassie Fitzherbert has a secret. When she was at school, she and her friends were responsible for the death of a fellow pupil. Decades later, Cassie is happily married and loves her job as a police officer.
Her husband persuades her to go to a school reunion and another ex-pupil, Garfield Rice, is found dead, supposedly from a drug overdose. As Garfield was an eminent MP and the investigation is high profile, it's headed by Cassie's new boss, DI Harbinder Kaur. Trouble is, Cassie can't shake the feeling that one of her old friends is behind it.
Is Cassie right, or was Garfield murdered by one of his political cronies? It's in Cassie's interest to skew the investigation so that it looks like the latter and she seems to be succeeding.
Until someone else is killed...