1x14 - Sonic Underground

A faction of the Freedom Fighters is wiped out by a swarm of metallic fly-bots. When Manic goes in search of the insects, he is stung with serum, making him loyal to Robotnik. Sonia finds Manic communicating a radio message to Robotnik and realizes her brother is under a spell. It is up to Sonic to exterminate the metallic pests.