The novel revolves around a plot to retrieve the buried treasure of nefarious pirate Red Ned Ockham.

The treasure, which is estimated to be worth close to two billion dollars, reputedly includes "St. Michael's Sword", a weapon with the power to kill anyone who looks at it.

No characters seen or mentioned in Riptide have any role in any of their other novels, unlike their other stand-alone works such as Mount Dragon, Thunderhead, and The Ice Limit.

Mysterious accidents, illnesses and computer problems plague the salvage team, and it is discovered that the architect of the "Water Pit" is more clever than anyone realized.

However, the team learns too late that the entire island is sitting over a massive natural void in the ground, and that anyone removing the sword will collapse it.

[2][3] Publishers Weekly wrote a mostly favorable review for Riptide, criticizing it for its "diffusion of villains" while also stating that "Machine-gun pacing, startling plot twists and smart use of legend, scientific lore (including cryptanalysis) and the evocative setting carry the day, however, resulting in an exciting boys' adventure tale for adults that's bound to be one of most popular of the summer reads.