Derek and the attendings go out to celebrate when he gets the grant he needs for his clinical trial; Meredith and Alex must fend for themselves during the night shift.
The BAU are called to apprehend a killer who has struck Detroit for the past three years during Devil's Night, the notorious pre-Halloween celebration.
Abby confesses that she's the mysterious saboteur warning other women to stay away from Barney but she reconciles her differences with him when they both realise that they have a shared hatred of Ted. They go to the bar and flaunt their faux romance but when Barney goes overboard and proposes to Abby, she takes his offer seriously.
Jake disappears with the daughter of Charlie's neighbor, a former NFL player (guest star MICHAEL CLARKE DUNCAN), and Charlie is left to cover his back. Meanwhile, Alan scores a hot date with the help of Charlie's Mercedes.
Heads of state gather at the UN to sign the accord, three at CTU make a final effort to expose a conspiracy, Logan and Pillar tie up loose ends, and justice may elude Jack.
