When a young woman is found brutally murdered in a parking garage, with a veritable mountain of potential evidence to sift through, it may be the most challenging case former NYPD detective Lincoln Rhyme has ever taken on.

A small jet with only one pilot onboard crashes into the Atlantic Ocean. Local authorities are unsure whether the cause of the crash is a bomb or a violent storm. The case seems like it will be an easy one to solve for former NYPD Homicide Detective Lincoln Rhyme to solve. The evidence is inside the cockpit but there is one problem. The wreckage sits at the bottom of the Puerto Rican Trench, the deepest part of the Atlantic Ocean that stretches to twenty-eight thousand feet. The plane can’t be raised. And there’s no way to get to where the evidence lies.

When the FBI comes to Lincoln Rhyme with the news that a mysterious assassin is targeting him, the detective is not particularly concerned. With his long career putting away criminals, he is accustomed to threats on his life, and has designed his Upper West Side townhome to be secure against nearly any threat. But when the assassin gets too close for comfort, shadowing Rhyme and his wife Amelia Sachs as they go about their daily life, Rhyme determines to find out why this person is after him. He must put himself inside the mind of a killer in order to save his own life, and possibly the lives of those he loves most.

Lincoln Rhyme and Amelia Sachs return to New York City to confront a killer terrorizing couples at their happiest — and most vulnerable.

In the early hours of a quiet, weekend morning in Manhattan’s Diamond District, a brutal triple murder shocks the city. Lincoln Rhyme and Amelia Sachs quickly take the case. Curiously, the killer has left behind a half-million dollars’ worth of gems at the murder scene, a jewelry store on 47th street. As more crimes follow, it becomes clear that the killer’s target is not gems, but engaged couples themselves.

The Promisor vows to take the lives of men and women during their most precious moments — midway through the purchase of an engagement ring, after a meeting with a wedding planner, trying on the perfect gown for a day that will never come. The Promisor arrives silently, armed with knife or gun, and a time of bliss is transformed, in an instant, to one of horror.Soon the Promiser makes a dangerous mistake: leaving behind an innocent witness, Vimal Lahori, a talented young diamond cutter, who can help Rhyme and Sachs blow the lid off the case. They must track down Vimal before the killer can correct his fatal error. Then disaster strikes, threatening to tear apart the very fabric of the city — and providing the perfect cover for the killer to slip through the cracks.

A killer without limits

He comes into your home at night. He watches you as you sleep. He waits.

A city in turmoil

He calls himself ‘The Locksmith’. No door can keep him out. No security system can catch him. And now he’s about to kill.

A race against time to stop him

Nobody in New York is safe. Now it’s up to Lincoln Rhyme to untangle the web of evidence and catch him.

But with Lincoln under investigation himself, and tension in the city at boiling point, time is running out...