S4·E4 The Most Dangerous Enemy

Steve and Rudy go to check up on scientist, Cheryl Osborne, who was performing research on chimpanzees but who has ceased communications. When they arrive they find something has destroyed the lab, and Rudy is bitten by a rampaging chimpanzee. Rudy begins to turn psychotic and Steve must both stop him and find Osborne before it's too late.