The team is in need of gravitonium to seal the tears in the universe leading to the Fear Dimension. The search leads them to Tony Caine, an old friend of Mack. Caine, in turn, directs them to a scientist named Dr. Getty, who had been forced to work for Hydra.
Getty reveals that the gravitonium they're looking for was on a ship that went missing and presumably sank during a storm. Fitz, despite his efforts, cannot locate the ship until Deke suggest that maybe the cargo caused the ship not to sink, but to float.
They indeed discover the ship high in the air. They are able to recover the gravitonium, and Mack fights with a mech as they escape the now-plummeting ship.
Back at the Lighthouse, the Fear Universe continues to leak, conjuring up Deke's mother, who quotes something her own mother used to tell her. Later, when Simmons says the exact same line, Deke realizes that Fitz and Simmons are actually his own grandparents.
Though he doesn't reveal this new information to the newlyweds, he happily helps them fix the tear.
Caine leaves to look into the old Deathlok program as the rest of the team returns from their trip to retrieve the gravitonium. Mack has purloined the mech's arms to replace Yo-Yo's missing limbs.