Sierra Clark's twin sister died on a cruise ship when she was eight. Three years later, Sierra's father takes 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 onboard the ship, under the care of his aunt. Harrison and Sierra become friends, despite their differences, while Sierra struggles with the reality of being on a cruise ship terribly similar to the one her sister died on. One day 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 onboard 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 true identity of the murderer, and the truth that stabs deeper than a knife, hiding in the shadows of The Legend.