A troubled ocean, a steel-gray sky, a landscape where sunshine turns and storms come in the blink of an eye. Bolton's thriller focuses on 28-year-old world-expert glaciologist Felicity Lloyd, who at the end of the summer stands high on Konig Glacier on the remote island of South Georgia. She's just finished reading a letter: She's finally she's been found, and her nemesis might be arriving on a cruise ship in the next few hours.

Grytviken, South Georgia is like a ghost town, and at night these ghosts seem to rise up and walk the streets again. Perhaps they're the whalers who ripped apart flesh and turned a deaf ear to the cries of pain. For Felicity's nemesis, Freddie, South Georgia is more beautiful than he ever imagined. For Bamber, the other narrator in Bolton's tale, Grytviken is the special place she goes to when the rage builds, almost tearhing her head apart. Only in The Petrel, the beached whaling ship in Grytviken Harbor, does Bamber find solace.

Troubled Felicity escapes to Bird Island, where she hopes she can put herself beyond Freddie's reach after being so sure she'd left the madness behind in Cambridge. Bolton keeps the reader's attention firmly on Felicity as the action moves to an unseasonably warm Cambridge, where the River Cam winds its way through trailing willow fronds and into the claustrophobic heart of the medieval city. Felicity's decision to travel to South Georgia coincides with a murder on Midsummer Common and the introduction of Felicity's therapist, Joe Grant, and Joe's detective mother, Delilah, who is tasked with investigating the City's first murder in "god knows how long." Someone has been attacking Cambridge's "rough sleepers." No one knows anything about the first victim, Bella Barnes. There are no witnesses and "bugger-all physical evidence."

In a now-familiar style, Bolton's tale unfolds around Felicity and Joe--their days in Cambridge, the last trace of a dream. In Felicity's confessionals to Joe, she remembers what the voice in her ear said to her: "It really is like someone else--someone invisible is living in my house." Joe thinks back on Felicity's symptoms: fugue states, amnesia, hearing voices and the belief that she's being stalked.

As the narrative voice alternates among Felicity, Joe, Freddie and enigmatic Bamber, each of them uncovers different threads. The story knots and tangles around them before completely unraveling on the great glacier. In Cambridge, Felicity can't explain the man who haunts her dreams, this man called "Freddie." She has loved him with all her heart, but he has caused her unbearable pain:

He's coming, the woman in her head says. You can't get away from him. He'll always find you.

While Joe tries to help, Felicity turns to South Georgia where she hopes to find some breathing space, time to think about what she really wants. The warning voices in Felicity's head are proven right; her fears of a stalker are revealed by Joe's hypnotherapy. She's not the Felicity Joe has come to know, though the unsettling edge is still there,floating like toxic weeds beneath the surface. Joe, meanwhile, has a complicated relationship with his mother. Delilah thinks Felicity might be a murderer, though Joe finds himself bonding with Felicity, dreading the mounting evidence of her guilt and the monster Freddie who shadows Felicity's days like a waking nightmare, both in Cambridge and later again in South Georgia.

Though not as tightly plotted as her previous novels, in The Split Bolton mostly creates an isolated sense of place, first in South Georgia, then in Cambridge. Felicity's conflicts are hidden in her past. That Freddie is not who we think is central to all that happens in The Split's climax. It may be a cliché that binds Felicity, Freddie and Bamber together, but they are unique enough to exercise a firm grip on our attention as we turn back to the glacier and its latent, ominous darkness.