All the Colors of Darkness by Peter Robinson

DI Annie Cabbot is called to the scene of a hanging in Hindswell Woods in Yorkshire. The man, Mark Hardcastle, appears to have committed suicide. The investigation becomes a bit more complex when Hardcastle's lover, Laurence Silbert, is found dead in his home. To the police, it seems to be a murder-suicide, although Annie and DCI Alan Banks are not as ready to close the case as their superiors are. They find out that Silbert is retired from M16. Are police higher-ups being pressured to move on? Is it possible that someone gave Hardcastle a "gentle push" to be a jealous lover, which led to Silbert's death? Alan and Annie work secretly to uncover the truth--at times putting their careers and lives on the line. Another solid police procedural in this long-running series. All the Colors of Darkness will be published in February.