Nick and H.E.A.T. go deep beneath the sea in order to investigate the mysterious disappearance of noted scientist Dr. Alexander Preloran and his own research team, and there H.E.A.T. discovers a hidden spacecraft belonging to a race of advanced, hostile non-humanoid aliens that hope to conquer the Earth with the help of a pet giant monster.

Tatopoulos finds a way to free the H.E.A.T. team from the telepathic control of the aliens via disrupting the tachyon emissions which the octopoid extraterrestrials use to control minds [actually, tachyons are hypothetical sub-atomic particles, mentioned frequently in sci-fi shows such as the various Star Trek series, which have the unique property of traveling backwards in time, and thus have nothing to do with psychic phenomena, but instead tend to be present in time travel phenomena and chronal anomalies of various sorts; it would have been more realistic to have the aliens utilize technology that generated psions, another very hypothetical particle, which is said to carry psychic energy, and is believed by some parapsychologists to be responsible for various psychic phenomena such as telekinesis, precognition, telepathy, etc., and thus could indeed affect organic brains in such a manner as to control them].