Murdermek, a death droid weapon, is sent back to Metropolis during Superman's time. OMAC, the one-man army corps, travels back to that time, too, to help Superman in "The Once and Future War."

OMAC crashes through the wall of an underground Intercorp laboratory. As Brother Eye broadcasts more power to him, OMAC fights his way to Intercorp's Time-Transmitter. The Intercorp scientists activate the Time-Transmitter, sending their robot assassin, Murdermek, back to the 20th Century. Before the Time Transmitter can self-destruct, OMAC leaps in after Murdermek. In Metropolis, police officers have Nick Bravo, and his gang, surrounded and pinned down inside a liquor store. Bravo opens fire on the police, who retaliate in kind. Murdermek appears in the liquor store. One of Bravo's gang opens fire on Murdermek, and is, summarily, put down. Once Murdermek ascertains that it's primary target is not present, it's exits into the street. Murdermek lays waste to the police, as it moves out into Metropolis. Superman intervenes, and fights a pitched, albeit brief, battle with Murdermek. After collapsing a building on the Man of Steel, Murdermek moves on. Seeing an opportunity for escape, Bravo and his gang follow in Murdermek's wake. OMAC appears. When the police attempt to detain OMAC, they are quickly put down. Having uncovered himself from the building debris, and witnessing OMAC's assault on the officers, Superman attacks OMAC. Despite his best efforts, OMAC quickly realizes that he is no match for the Man Of Steel. OMAC convinces Superman to stand down, then explains who he is, and why he has come to the 20th Century. At that same moment, Murdermek is also filling in Bravo's gang about it's mission, to assassinate OMAC's ancestor, and thus prevent the One Man Army Corps from ever being created.

Murdermek locates it's target, Norman Blank, at the Metro Central Station. Murdermek immediately fires a barrage of missiles on it's target, but Superman rescues the man, in the nick of time. Leaving the man in a place of relative safety, Superman engages Murdermek. With Superman locked in combat with Murdermek, Bravo and his gang, outfitted with high tech weaponry, close in on Murdermek's target. OMAC intervenes, drawing their fire, then quickly taking out one of Bravo's men. In the World That's Coming, the Brother Eye satellite, having lost it's connection to OMAC, remote rebuilds the Time-Transmitter, from orbit. Superman is barely able to hold his own against Murdermek. Despite his best efforts, he just cannot put Murdermek down. Finally, Superman puts every last ounce of raw power he can muster into an epic haymaker, felling Murdermek. Superman reconnects with OMAC, who has already defeated Bravo, and his gang. Superman introduces OMAC to his ancestor, only to discover that the man they've been protecting is not Norman Blank. Before either man can truly react, OMAC is drawn back to the World That's Coming, by the Time-Transmitter. Superman is left to puzzle over a mystery, while the real Norman Blank, a janitor, who had been standing behind the man Murdermek targeted, sweeps up the battle debris.