From the inside flap:
"Two cousins, irreversibly damaged by a childhood prank whose devastating consequences changed both their lives, reunite twenty years later to renovate a medieval castle in Eastern Europe, a castle steeped in blood lore and family pride. Built over a secret system of caves and tunnels, the castle and its violent history invoke and subvert all the elements of a gothic past: twins, a pool, an old baroness, a fearsome tower. In an environment of extreme paranoia, cut off from the outside world, the men reenact the signal event of their youth, with even more catatrophic results. And as the full horror of their predicament unfolds, a prisoner in jail for an unnamed crime, recounts an unforgettable story -- a story about two cousins who unite to renovate a castle -- that brings the crimes of the past and the present into piercing relation."
This is a milestone in haunted-house fiction, both stylistically and in terms of narrative. Not only does she eschew quotation marks when her characters talk (much like Cormac McCarthy), but she utilizes multiple POVs [points of view], especially at the twisty finish, masterfully rendered.
The above elements aren't the main reasons why this novel wowed me. It's how Egan balanced the "guilt = haunted" equation with surprising and effective moments of spine-freezing terror. And the characters are full of conflicts, doubts, guilt and other emotions, rich soil in which to plant seeds of shadows-out-of-the-corner-of-your-eye fear moments.
Unputdownable and landmark, this. By all means, own this.