Defending Darkheart, Parts 4.Grimlord, knowing Dark Heart/Tyler is gravely injured, launches a full aerial assault on Professor Hart's lab, as this is the first place Ryan will take his father. Ryan, warned that the lab is under attack, takes his father to a long forgotten and secret lab in the mountains. Father and son are about to be attacked by a full scale aerial assault when J.B. reinputs the transformation commands into the lab's computer. He and Kaitlin transform and rush to Ryan and Dark Heart/Tyler's aid. Ryan and Dark Heart/Tyler decide to challenge Grimlord face to face and enter virtual reality. Meanwhile, Grimlord begins a self-destruct system. Father and son escape just as Grimlord's dungeon explodes -- supposedly with Grimlord inside. However, most of the mutants were outside, and another battle begins. Ryan fights off Decimator and Tyler returns to human form. Ryan holds his father before he disappears -- as Grimlord takes him back to Virtual World.