The Angle's Game by Carlos Ruiz Zafron

The Angle's Game - In an abandoned mansion at the heart of Barcelona, a young man, David Martin, makes his living by writing sensationalist novels under a pseudonym. The survivor of a troubled childhood, he has taken refuge in the world of books and spends his nights spinning baroque tales about the city’s underworld. But perhaps his dark imaginings are not as strange as they seem, for in a locked room deep within the house lie photographs and letters hinting at the mysterious death of the previous owner.