The Wych Elm — Tana French

Our Thriller of the Month for September 2019
For me it all goes back to that night, the dark corroded hinge between before and after, the slipped-in sheet of trick glass that tints everything on one side in its own murky colours and leaves everything on the other luminous and untouchable.
One night changes everything for Toby. He's always led a charmed life - until a brutal attack leaves him damaged and traumatised, unsure even of the person he used to be. He seeks refuge at his family's ancestral home, the Ivy House, filled with memories of wild-strawberry summers and teenage parties with his cousins.
But not long after Toby's arrival, a discovery is made: a skull, tucked neatly inside the old wych elm in the garden.
As detectives begin to close in, Toby is forced to examine everything he thought he knew about his family, his past, and himself.
A spellbinding standalone from a literary writer who turns the crime genre inside out, The Wych Elm asks what we become, and what we're capable of, if we no longer know who we are.