While on a trip to the aquarium, the Power Pack confronts a dangerous creature from another planet.
Out at sea, a fishing vessel has caught a large… something. After hauling it in, a huge serpent breaks free and the crew falls asleep under its gaze. The captain is also a victim, but he hits the foghorn as collapses and the tone of the horn puts the serpent to sleep.
Weeks later, the Power children are preparing for a night out with their friend, Friday, a sentient Kymellian spaceship. They meet in the park and Alex muses on the odd happenings in the papers. One might even look so far as the local aquarium that has become home to an odd sea serpent. Friday notes the serpent and remarks that it looks a lot like a Xanthian Boulder Crusher. Friday explains that the Boulder Crushers gaze can put its prey to sleep while it eats. With that, Friday then retires for the night at the bottom of the Hudson River.
The next day, the Power kids meet their grandpa and reluctantly head to the aquarium. On the train, Katie tries to learn how to play her grandpa’s oboe with little luck. At the aquarium, the Power kids see the sea serpent that is still in its deep sleep. It being less-than interesting, the kids move to the submarine exhibit. There they find Friday hiding.
Back at the sea serpent tank (which is not enclosed), Katie resumes her practice of the oboe. A certain note seems to wake the serpent and it immediately begins putting people to sleep with its gaze. Acting quickly, the Power Pack removes any potential victims before attempting to deal with the sea serpent, which they have reason to believe is the aforementioned Xanthian Boulder Crusher. Head-on attack is futile, as the serpent is either too strong or two fast. The kids come up with a plan.
Heading to the submarine exhibit, the Power Pack plans on using one of the shiny subs on the serpent in hopes that seeing its reflections will cause it to fall under its own sleep spell. Katie disintegrates a piece of the sub. Upon encountering the serpent again, both Jack and Katie get a full blast from the serpent and fall asleep. Friday shows up and explains how Boulder Crushers are immune to their spells. The mirror idea futile, Alex and Julie then degravitize the monster and whip him out to sea.
Back at the aquarium, Alex and Julie meet Marrina. She is on a mission to stop the serpent (it having previously attacked her) and Alex volunteers the aid of the Power Pack. Once Jack and Katie awaken, they also agree to hunt the sea serpent.