Sierra Clark's twin sister died on a cruise ship when she was eleven. Four years later, Sierra's parents take her to a vacation on a brand-new cruise ship, The Legend, in an effort to help her overcome her sister's passing. Harrison Walker, an energetic farm boy from Texas, meets Sierra aboard the ship, under the care of his aunt. Harrison and Sierra become friends, despite their differences, while Sierra struggles to enjoy the cruise and overcome the weight of memory and loss.

Two days after The Legend leaves the mainland, disaster strikes.

A passenger aboard the ship is murdered, and no one knows who committed the crime. Panic ensues aboard The Legend, and while efforts are made to find the perpetrator, more victims die. Harrison and Sierra find themselves stranded in the middle of the ocean, trapped on the ship with a murderer. But far more terrible is the truth that stabs sharper than a knife hiding deep inside The Legend.