Three men take the place of Batman while the real Caped Crusader is away, as part of an "If I Were Batman" contest run by the Gotham Gazette, and gangsters attempting to break John Larrow out of jail intend to capitalize on the occasion.
Synopsis for "The Strange Experiment of Dr. Erdel"
When Dr. Erdel uses a “robot brain” and teleportation system of his creation to capture and retrieve something from space, it brings a green-skinned Martian named J’onn J’onzz to Earth. After both introduce themselves to each other, J’onzz asks Erdel to return him to Mars. Erdel replies that he cannot do that, since it might take years to reverse his computer’s program. The Martian, knowing he must adapt his appearance to that of humans, uses his chameleon-like powers to make himself look like a brown-haired Caucasian human male. Seconds afterward, the shock of the preceding events takes its toll on Erdel’s weak heart. With his last breaths, Erdel asks J’onzz to forgive him for making him a prisoner of Earth. Then he dies.
J’onzz muses that the Martians are working on a “Project Star-Ride” for interplanetary travel. But until that project is completed--however long that may take--he is bound to Earth. He Americanizes his name to John Jones. Then, going to the seaside, he uses his Martian mind-over-matter power to extract gold from seawater to give him working capital. John Jones then takes a tour of the Earth, sometimes using his powers of invisibility and immateriality to conceal his presence.
One aspect of Terran life disturbs J’onn J’onzz: crime. Since Earth is a younger planet than Mars, and since Mars underwent the “Great Evolution” centuries ago that virtually wiped out crime, its rate of wrongdoing is much less than that of Earth. J’onzz decides to help the Earthmen by fighting crime. In his John Jones identity, he takes and passes a detective exam at the Midtown police department. But he realizes he must avoid a Martian’s one weakness--fire, which can sap his powers and take his life.
Originally, Doctor Saul Erdel was shown to have died in this issue. However, Martian Manhunter (Volume 1) #2 reveals that had faked his death following the events from this issue, and continues to live out of his small cabin in Colorado.
Martian Manhunter (Volume 1) #3 shows that the Martian Manhunter arrived on this world carrying the body of his dead daughter K'hym in his arms. The inclusion of K'hym into the Manhunter's origin is a retcon and was never part of the original origin story. Later revisions of J'onn's origin suggest that K'hym actually remained on Mars after she died, and never accompanied J'onn to Earth at all.
Trivia
Although the Flash (Barry Allen) is generally accepted as the first Silver Age DC Comics character, the Martian Manhunter actually precedes the first appearance of the Flash by almost a year.