Having recently discovered that he fathered twins 23 years ago, Dirk Pitt joins forces with his offspring, both of whom have inherited his love of the sea, and embarks on a dangerous mission. Dirk, his daughter Summer, and his son, who is also named Dirk, investigate a mysterious brown tide that has washed up on the shores of Nicaragua. While there, the trio, along with the crew of the NUMA ., face an evil worse than anything they could have ever anticipated.