A boating trip turns into a nightmare for five teenagers when they happen upon an abandoned yacht. Curious, the teens hop aboard, and two, Bob and Julie, decide that the yacht is a perfect place for some illicit lovemaking, despite the presence of a bizarre biology laboratory. Unfortunately, the amorous couple become infected with radioactive plankton, turning Bob into a flesh hungry monster who greedily devours his lover. Soon, other monsters have come up from the deep to hunt down the three remaining teens.