Smoke and Whispers (Oxford Investigations #4) by Mick Herron; 2015. Softcover.

Oxford private detective Zoë Boehm turns up dead in Newcastle, launching her friend Sarah Tucker into an investigation with several leads—but no one she can trust. When a body is hauled from the River Tyne, Sarah Tucker heads to Newcastle for a closer look. She identifies the dead woman as private detective Zoë Boehm, but putting a name to the corpse only raises further questions. Did Zoë kill herself, or did one of her old cases come back to haunt her? Why was she wearing the jacket a murderer had stolen years before? And what’s brought Sarah’s former sparring partner Gerard Inchon to the same broken-down hotel where she’s staying? Coincidence is an excuse that soon appears pretty unconvincing. Sarah can’t leave until she’s found the answers to her questions, however dangerous they might turn out to be.