STFUandPLAY's Romudeth writes:
The prison is overrun by zombies after a mystery person opens up one of the gates. This person turns out to be Andrew, the prisoner that Rick thought he sent to his death in episode two. Andrew managed to escape that courtyard full of zombies and came back to take revenge on Rick and the group. Andrew ended up dying after being shot in the head by one of this fellow inmates but the damage was done. By the end of the episode, two of the regular cast was dead.