As of now, The Walls of the Castle by Tom Piccirilli is free at Amazon (US, ES). This is the synopsis of the book:
From four-time winner of the Bram Stoker Award, two-time winner of the International Thriller Writers Award and finalist for the 2009 Edgar Allan Poe Award Tom Piccirilli comes an intense and visceral psychological thriller novella, the first title in the Black Labyrinth imprint illustrated by Gothic artist Santiago Caruso.
An atmospheric yet action-packed, mature psychological thriller that is part examination into the bonds of family and part treatise on the nature of identity, The Walls of the Castle explores the deepest areas of what makes us who we are. With a noir sensibility and complexity of character, the novella is a hybrid psychological thriller that's part suspense tale, part family saga, and part literate mystery.