Mumm-Ra summons Malcar, an ancient alchemist, to return from the dead. The alchemist returns old and weak, as he was when he died. Mumm-Ra takes him to the canyons of youth to restore his youth and power.
On regaining his powers, Malcar uses them against the Thundercats. He transforms all the Thunderillium on the planet into Thundrainium, therefore weakening Lion-O. Lion-O had been looking for Thundrillium for the Thundertank to save Bengali and Snarfer, trapped in a cave. In this weakened state, Lion-O is unable to send the Thundercat signal.
Fortunately Jaga appears and uses the sword of Omens to restore the Thundrillium and at the same time, makes Malcar old and weak again. Mumm-Ra must send Malcar back to the Canyons of Youth.
While Malcar is in the Canyons of Youth, Jaga appears in Mumm-ra's pyramid and distracts him. Malcar ends up getting younger and younger, all the way back to babyhood. This destroyes Malcar's powers, defeating Mumm-ra.