Tang and Cooper?'s past physical problems are put to the test when they are attacked on the street by a ?perp.? Lydia and Ruben investigate a convenience store murder, and Lydia uses her typical compassionate charm to collect facts on her suspect from an unassuming grandmother (guest star MARLA GIBBS). Ben and Sammy ride with another officer who is prone to small mistakes. And Joel Rucker (guest star CARL LUMBLY) takes over as the new captain.