What writer Benjamin Constable needs is a real-life adventure wilder than his rampant imagination. And who better to shake up his comfortable Englishman-in-Paris routine than the enigmatic Tomomi "Butterfly" Ishikawa, who has just sent a cryptic suicide note?

She's planted a slew of clues--in the pages of her journal, on the hard drive of her computer, tucked away in public places, under flowerpots, and behind statues. Heartbroken, confused, and accompanied by an imaginary cat, Ben embarks upon a scavenger hunt leading to charming and unexpected spaces, from the hidden alleys of Paris to the cobblestone streets of New York City.

But Butterfly's posthumous messages are surprisingly well informed for the words of a dead person, and they're full of confessions of a past darkened by insanity, betrayal, and murder. The treasures Ben is unearthing are installments of a gruesome memoir. Now he must draw a clear line between the real and surreal if he is to save himself, Butterfly,...