Death of an ordinary man - Glen Duncan

Nathan's gravestone offers a short and hopeful summary: At rest. But Nathan is not at rest, and knows he won't be until he can find out how and why he died.
A spectral spectator throughout the day of the wake, he listens to his wife, son, daughter, father and best friend, getting to know them like he has never known them before. But there are two things he can't understand: a strange young couple on the fringes of the wake, whose presence fills him with dread; and a room in his house he never knew existed, with a door he feels compelled to open. A door that he knows will lead to a terrifying secret.