"The Batman: Lost Heroes" is the 65th episode and the series finale episode of the series The Batman. The episode first aired on Kids WB! on March 8, 2008 as a one-hour movie. The episode was part of the Justice League season in which Batman would team up with another hero in the fifth season.
As the episode opens, Batman and Superman are trying to capture Toyman. During the fight, bombs go off, and as the smoke clears, Batman finds that Superman is missing. At the same time, Flash and Green Arrow are trying to find Mirror Master. The two defeat him in a carnival house of mirrors, but from behind the mirrors, barrels open to release a gas that knocks out both heroes. Just before he blacks out, Green Arrow sees Flash being dragged away.
At the Batcave, Batman, Green Lantern, and Green Arrow convene with Martian Manhunter and Hawkman had been taken to. The remaining Justice League concludes that Batman and Green Arrow were not taken because they have no superpowers. When the Justice League goes in search of Superman and Flash at the carnival, they are attacked again, this time targeting Martian Manhunter with fire and Green Lantern with electric droids. Batman and Green Arrow put out the fire, but their comrades are gone when the smoke clears.
While working on trying to find the heroes using the strange radio transmitters from the barrels that knocked out Flash and Green Lantern, Batman falls asleep. He has a vision of the five kidnapped Leaguers restrained and glowing with power, and an apparition of the Martian Manhunter repeats to him the name "Hugo Strange."
Batman & Robin along with Green Arrow go to Arkham, where Dr. Strange is supposedly incarcerated. However, the inmate they meet is not Strange himself but an alien robot duplicate. Together, the heroes disable the robot, and Batman retrieves its radio transmitter. Tracking the transmitter's signal, the three remaining heroes arrive at an air raid bunker, which they break into; they are promptly captured by the real Hugo Strange, who was hiding out there.
Dr. Strange smugly reveals the captured Justice Leaguers, each of whom has a tube attached to his chest carrying blue light away from him. Strange discloses that he is working with aliens called The Joining, who invaded Earth before but were stopped by the Justice League. Strange proposed to help The Joining by disabling the Justice League in exchange for the "knowledge of the Universe."
Batman & Robin with Green Arrow manage to break free of their restrains and cut loose their friends as well. When they do, they unveil five androids, each of which has taken on the powers of one of the kidnapped Leaguers. When the Justice League tries to fight back, they discover that the kidnapped superheroes--Superman, Green Lantern, Hawkman, Flash, and Martian Manhunter--no longer have their powers at all. To their advantage, however, the androids still cannot use the heroes' stolen powers to their full extent. Unable to fight the androids successfully, the League escapes Strange's hideout in a stolen Joining aircraft, which Batman pilots to a secure location to regroup and meet up with Batgirl.
In the hideout, Batman gives each de-powered hero a weapon that he has made to neutralize their powers--to Superman a Kryptonite gun, to Green Lantern a gun that shoots yellow powder, and so forth. The League, backed up by Robin and Batgirl on jetpacks, set out to ambush the androids, which are destroying Gotham City to find them. The weapons work, but only temporarily disable the androids, until Robin discovers that the androids have a weak spot on their chests. The heroes each smash the stolen symbols on the androids' chests and reclaim their powers. Meanwhile, Hugo Strange tells The Joining that he has done his part as promised, and demands the knowledge of the Universe. A member of the Joining comes through a portal and gives him what he asks for.
Re-powered, the League returns to Strange's lair, only to find him in a vegetative state, his brain overwhelmed by the influx of knowledge. From Strange's mind, the Martian Manhunter gleans that the invasion fleet is on its way. Superman and Green Lantern go to meet the mothership as it approaches, fighting swarms of The Joining fighters that fire Kryptonite blasts and yellow energy. Flash and Green Arrow also go to fight the craft that make it to the surface. However, there are too many to fight at once, so Batman suggests using the knowledge in Strange's mind to send a virus to the entire Joining.
As they begin, the giant, robotic creature who gave Strange his knowledge reappears, attempting to kill Strange before the League can use him. Batman & Robin go to engage it, leaving Batgirl to help the Martian Manhunter reprogram the Joining transmitter. Batman & Robin fight with the alien, but they chase it into the superpower transfer room, and some of the superpowered energy material left in the tubes drip onto it. The alien grows, glowing with green energy and moving with super-speed; Batman and Robin alone are no match for it. The alien dispenses with them and moves on to attack the Martian Manhunter as he extracts the last bit of information from Strange. At the last moment, Batgirl finishes the sequence; the alien shuts down at the same moment that all of The Joining fighters go dead, crackling with blue electricity. The fighters fall into Gotham Bay, while Green Lantern flings the Joining mothership into the Sun.
The Justice League reconvenes in the Watchtower to witness the mothership explode. Superman acknowledges that even with their superpowers, the Justice League could not have triumphed without Batman and Green Arrow's participation. Green Arrow, who had been bitter about the power/no power distinction before, simply remarks that "Some of us need powers--and some of us don't."
The episode comes to a close with Batman & Robin alongside Batgirl in the Watchtower with the final lines spoken in the series having taken place.
Robin: "We have the coolest clubhouse."
Batgirl: "Yeah! Junior Justice League: Teen Division."
Batman grins saying to them "Nice try." as all three of them look down on Earth from the Watchtower.
- Batman: Rino Romano
- Robin: Evan Sabara
- Green Arrow: Chris Hardwick
- Batgirl: Danielle Judovits
- Martian Manhunter: Dorian Harewood
- Green Lantern: Dermot Mulroney
- Hawkman: Robert Patrick
- Flash: Charlie Schlatter
- Superman: George Newbern