Born a year apart, May and June Anderson were once as close as twins. Time and a loveless marriage changed the once vibrant May into June's timid counterpart. Now, two years after June abruptly disappeared, May receives a letter from her sister, inviting her to visit a mysterious colony in southern California. Eager to match June's boldness for once, May doesn't hesitate.

The Colony is located in a magnificent Spanish Revival-style mansion perched on a bluff overlooking the Pacific, and is presided over by the group's charismatic leader, Rex. Colony members believe in an afterlife where departed souls mingle, and that the truly enlightened can even summon back the spirits of lost loved ones. May is told that June has recently left on a mission, and she's intrigued enough to accept Rex's invitation to stay until her sister's return.

Drawn deeper into the group, and under Rex's seductive spell, May undergoes their initiation ceremony. Yet her questions grow more urgent with June's continued absence—and the warnings of a presumptuous but charming undercover investigator. May has longed for the daring, adventurous life her sister pursued, but her arrival has sparked a dangerous unraveling within the Colony, where nothing and no one is quite as it seems.