Mercenary Pursuits is the fourth episodes of the Beast Machines TV series.
Optimus Primal contemplates the images of Rhinox and Silverbolt and vows to find them. His meditation is interrupted when he senses the presence of a spark; the team goes out to find it. During the search, Rattrap beaks into a secure laboratory and discovers the transformation inhibitor virus which Megatron used... and a counter-virus as well, a transformation enhancer. Rattrap swipes the enhancer while Cheetor's back is turned.
While Thrust and Jetstorm squabble, Tankor manages to find the Maximals, who elude him by reverting to beast mode... until Rattrap shows up, able to transform at last thanks to the enhancer. This alerts Tankor, of course, who attacks the team. Rattrap finds he's unable to control his transformations, as he continually changes between robot and beast mode, including some odd intermediate forms as well.
Tankor manages to trap the Maximals under a metal dome. Thrust and Jetstorm arrive and fight Tankor for the right to bring in the captive Maximals; the distraction allows the Maximals escape from the dome, but an explosion knocks out all the Transformers present, leaving only the durable Tankor standing.
At the Citadel, Megatron gloats to the captured Maximals, while Tankor demands his reward: "freedom" via the removal of his spark. Rattrap's continual transformations strain his bonds to the breaking point, freeing him; he quickly releases the others. During the ensuing fight, Megatron loses control and breaks free of his control harness; Primal talks directly to Tankor's spark, compelling him to do what is right. After a moment of confusion, Tankor blasts open the door so the Maximals can escape, and leaves with them.
Restored to his harness, Megatron interfaces directly with Tankor's CPU, deleting the last 20 cycles of his memory. Thus Tankor suddenly attacks the Maximals again as they travel underground; Megatron blocks Primal's attempts to speak to Tankor's Spark again. The Maximals trip up Tankor as he's preparing to fire; the cannon backblast sends him flying upwards through Cybertron's sublevels, only to crash back down to the surface atop a startled Thrust and Jetstorm.
Optimus Primal explains to the other Maximals that he sensed something familiar about Tankor's spark... but then it was gone.