Auld Acquaintance

"Auld Acquaintance" is the 26th and last episode of the first season of Young Justice, and the 26th of the overall series. It aired on April 21, 2012.

Logline
The Team finally learns the identity of the traitor in their midst, forcing a battle against an enemy more dangerous than any they've ever faced before!

Title
"Auld acquaintance" is part of the opening line of Auld Lang Syne, a song traditionally sung in celebration of the New Year in the English speaking world. This episode takes place on December 31 and the song starts playing with the stroke of midnight.

Cast and characters
! colspan="3"| Uncredited ! colspan="3"| Non-speaking roles
 * Lacey Chabert
 * colspan="2"| Zatanna
 * Crispin Freeman
 * colspan="2"| Red Arrow
 * Kittie
 * colspan="2"| Rocket
 * Stephanie Lemelin
 * colspan="2"| Artemis
 * Jesse McCartney
 * colspan="2"| Robin
 * Danica McKellar
 * colspan="2"| Miss Martian
 * Nolan North
 * colspan="2"| Superboy
 * Khary Payton
 * colspan="2"| Aqualad
 * Jason Spisak
 * colspan="2"| Kid Flash
 * Thom Adcox
 * colspan="2"| Klarion
 * Jeff Bennett
 * colspan="2"| Red Tornado/John Smith
 * Nick Chinlund
 * colspan="2"| Sportsmaster
 * Oded Fehr
 * colspan="2"| Ra's al Ghul
 * Miguel Ferrer
 * colspan="2"| Vandal Savage
 * Bruce Greenwood
 * colspan="2"| Batman
 * Vanessa Marshall
 * colspan="2"| Black Canary
 * colspan="2"| Red Tornado/John Smith
 * Nick Chinlund
 * colspan="2"| Sportsmaster
 * Oded Fehr
 * colspan="2"| Ra's al Ghul
 * Miguel Ferrer
 * colspan="2"| Vandal Savage
 * Bruce Greenwood
 * colspan="2"| Batman
 * Vanessa Marshall
 * colspan="2"| Black Canary
 * Bruce Greenwood
 * colspan="2"| Batman
 * Vanessa Marshall
 * colspan="2"| Black Canary
 * colspan="2"| Black Canary
 * colspan="3"| Captain Marvel
 * colspan="3"| Wolf
 * colspan="3"| Teekl
 * colspan="3"| Atom
 * colspan="3"| Hawkman
 * colspan="3"| Hawkwoman
 * colspan="3"| Martian Manhunter
 * colspan="3"| Plastic Man
 * colspan="3"| Wonder Woman
 * colspan="3"| Hawkman
 * colspan="3"| Hawkwoman
 * colspan="3"| Martian Manhunter
 * colspan="3"| Plastic Man
 * colspan="3"| Wonder Woman
 * colspan="3"| Plastic Man
 * colspan="3"| Wonder Woman
 * colspan="3"| Wonder Woman
 * colspan="3"| Wonder Woman
 * colspan="3"| Aquaman
 * colspan="3"| Amanda Spence
 * colspan="3"| Amazo (flashback)
 * colspan="3"| Black Adam (flashback)
 * colspan="3"| Brain
 * colspan="3"| Count Vertigo (flashback)
 * colspan="3"| Doctor Fate
 * colspan="3"| Dr. Desmond (flashback)
 * colspan="3"| Dubbilex
 * colspan="3"| Flash
 * colspan="3"| Garfield Logan (flashback)
 * colspan="3"| Garth (flashback)
 * colspan="3"| G-Elves
 * colspan="3"| A G-Gnome (flashback)
 * colspan="3"| Green Arrow
 * colspan="3"| G-Trolls
 * colspan="3"| Guardian
 * colspan="3"| Hugo Strange (flashback)
 * colspan="3"| Icon
 * colspan="3"| John Stewart
 * colspan="3"| Joker (flashback)
 * colspan="3"| Lex Luthor
 * colspan="3"| Mammoth (flashback)
 * colspan="3"| Match
 * colspan="3"| Monsieur Mallah
 * colspan="3"| Ocean-Master
 * colspan="3"| Psimon (flashback)
 * colspan="3"| Queen Bee
 * colspan="2"| Roy Harper
 * colspan="3"| Sphere
 * colspan="3"| Tula (flashback)
 * colspan="3"| G-Trolls
 * colspan="3"| Guardian
 * colspan="3"| Hugo Strange (flashback)
 * colspan="3"| Icon
 * colspan="3"| John Stewart
 * colspan="3"| Joker (flashback)
 * colspan="3"| Lex Luthor
 * colspan="3"| Mammoth (flashback)
 * colspan="3"| Match
 * colspan="3"| Monsieur Mallah
 * colspan="3"| Ocean-Master
 * colspan="3"| Psimon (flashback)
 * colspan="3"| Queen Bee
 * colspan="2"| Roy Harper
 * colspan="3"| Sphere
 * colspan="3"| Tula (flashback)
 * colspan="3"| Match
 * colspan="3"| Monsieur Mallah
 * colspan="3"| Ocean-Master
 * colspan="3"| Psimon (flashback)
 * colspan="3"| Queen Bee
 * colspan="2"| Roy Harper
 * colspan="3"| Sphere
 * colspan="3"| Tula (flashback)
 * colspan="3"| Queen Bee
 * colspan="2"| Roy Harper
 * colspan="3"| Sphere
 * colspan="3"| Tula (flashback)
 * colspan="3"| Sphere
 * colspan="3"| Tula (flashback)
 * colspan="3"| Tula (flashback)
 * colspan="3"| Tula (flashback)

Continuity

 * The flashbacks accompanying Batman's explanation of Red Arrow feature footage from "Independence Day", "Welcome to Happy Harbor", "Infiltrator" and "Usual Suspects".
 * Kid Flash mentions confiscating bio-chips off Cheshire, which happened in "Usual Suspects".
 * Aqualad talks of Tula, who broke his heart by striking up a relationship with Garth in "Downtime".
 * Red Arrow's explanation of his programming flashes back to the events from "Targets", and elaborates on those events.
 * Vandal Savage's speech features a flashback to "Revelation", "Downtime", "Terrors", "Usual Suspects", "Independence Day", "Drop-Zone", "Schooled", "Insecurity" and "Image".

Trivia

 * Main title clips:
 * Batman pulling a picture of Red Arrow
 * The Team looking incredulous
 * Aqualad kicking a door open
 * Superboy looking angry
 * Red Arrow taking aim
 * Artemis fighting
 * Number 16:
 * All three timestamps indicate 16 minutes.
 * The Starro-tech takes 0.16 nano-seconds to be fully assimilated by its host.
 * The six Leaguers were unaccounted for for 16 hours.
 * The group of Leaguers unaccounted for 16 hours—Superman, Batman, Wonder Woman, Martian Manhunter, Green Lantern and Hawkwoman—corresponds with six of the seven core members of the League in the Justice League animated series, though Hawkwoman replaces Hawkgirl. The seventh member was the Wally West version of the Flash.
 * This episode aired in Brazil on March 19.

Unanswered questions

 * What is "phase two" of the Light's plan?
 * What did the six Leaguers do and where did they go during the missing 16 hours?
 * Why were those six specific members chosen for that mission?
 * What happened to the real Speedy's right arm?
 * What will the Light do with Match and Speedy?