Shawn tags along with Gus to London for a Harry Potter Convention, but they are sidetracked by Interpol for an undercover assignment and reunion with a familiar face.
Mycroft shows up in New York to ask Holmes and Watson to solve a case concerning his former fiancée. Mycroft and Joan's relationship is a source of contention with Sherlock.
The League captures a dying Luthor, who breaks out of prison and assembles a group of villains to defeat the heroes.
A renegade Amazon, Aresia, leads a new incarnation of the Injustice Gang to accumulate the components for a bio-weapon.