Mackenzie Astin

Meredith and Derek's relationship concerns Zola's adoption counselor; Alex notices he has become an outcast; Cristina makes a difficult decision.

While Meredith faces the repercussions of messing with the medical trial, April tries to step up as chief resident; Cristina and Owen disagree.

After an infamous serial murderer is executed, women in the same Oklahoma town are attacked by a copycat; Prentiss gets nervous about making a major real estate purchase.

The team leads a class of college students through the nearly 20-year chase for a serial killer.

The team tries to prevent a viral outbreak during an investigation into a journalist's murder, whose infected body is found at a biohazard facility; when Arastoo Vaziri is affected by the mutated virus, the only way to save him is to solve the case.