Juliette's help is necessary because Schubert has set his sights on the acquisition of a strange an d ancient relic, a hawk statue that can cause power black-outs. The device is protected in an ancient underwater cave by booby traps.
Once Schubert gets his hands on the unusual device, Mark and Juliette must get it back, lest Schubert once more hold the world ransom.
But the hawk statue can also transform into a living hawk, as we see in the climactic act. There, it escapes from Schubert, and attacks Mark, and then flies away, never to be seen again.
In the time since the series has begun, we’ve seen him hold the world ransom with a microwave device, and create a sentient, out-of-control robot probe too. At the very least, there is enough evidence to consider him a “person of interest,” and it seems the Federal Government would want to hold him for his “proximity’ (if nothing else…) to several illegal and dangerous activities.
But “Hawk of Mu” seems more concerned with the funny/quirky Mutt and Jeff relationship between Mark and Schubert’s daughter, Juliette than in these other concerns of narrative and character. She accidentally causes Mark to be captured and sent to jail, but then assists him in escaping. Schubert, meanwhile, wants to know the water breather’s intentions towards his daughter.
More and more, one can see how Patrick Duffy’s sincere performance as Mark Harris is the (often-powerful) anchor that grounds Man from Atlantis and keeps audiences tuned in. Here he treats the quirky Juliette with respect and decency, and notes that he doesn’t “make fun” of people who are different. Instead, he finds her "charming."
The innocent, fish-out-of-water depiction of the character keeps Mark, and his series, generally appealing, even when the stories are baffling, or a letdown.
In terms of the Man from Atlantis's powers, we see in "Hawk of Mu" (as we did in the TV-movies) that he weakens when taken away from the water, and that he becomes rejuvenated, and scary strong, when he is in water. Here, when he is hit with the water from a hose in prison, he becomes physically powerful and bends the jail bars with his bare hands.