Paulino Nunes

While navigating the fallout from Katie's secret, Amy treats a critically ill patient with a dark one of her own; Jake is forced to hide the truth from Amy about Rachel's health scare; Richard returns with a trick up his sleeve.

On her last day at Westside, Joan chooses an unlikely successor, crowns a Chief Resident and imparts some final wisdom to the next generation; Gina steps in to help TJ's patient; Amy and Jake's tension intensifies while treating a pregnant teen.

A shocking turn of events ensues when Amy and Jake treat an expectant mother injured during a robbery; Michael is challenged to open up when Katie's therapist invites him and Amy to a session; TJ and Sonya help Julie navigate a mysterious illness and an unexpected romance.

Lt. Terry Clayton (guest star HENRY CZERNY -- The Tudors) of the 7th Mass arrives with word that the aliens are on their way to attack the 2nd Mass. Clayton's plan to lead the children to a safe haven while the adults remain behind to fight is met with some resistance from the parents, including Tom.

The Sisters of Mercy need Sydney's help to find the 400-year-old remains of a decapitated nun -- along with the treasure she guards.

While working on a high-stakes gun raid, Andy (Missy Peregrym) and Gail (Charlotte Sullivan) stumble upon a victim of domestic abuse (guest star Kristin Booth) whose brutal experience in the system has taught her not to trust the police.