Agents of the Society of Shadows infiltrate a retirement home and kidnap one of the elderly residents. They are interrupted by Batman and Robin (Dick Grayson ), but manage to escape with their captive.
Returning to the Batmobile to give chase, they find a cassette left on the seat. They play the tape, and hear Ra's al Ghul telling them a story:
In the year 1883, when the Transcontinental Railroad is about to be completed in the Utah territory. Elderly bounty hunter Jonah Hex visits the nearest town. Making the acquaintance of a local barmaid, he tells her he is hunting for a fugitive outlaw, Arkady Duvall. She recognizes him immediately, and says he has been driven out of town after beating up some of the local women. She has no idea where he is now, but when Hex asks if there's been any strange activity in the area, she mentions strange sounds and lights coming from a local mountain, and rumors of a dragon. She leads him to the mountain, and then he sends her back. Sneaking inside the mountain, he finds an impromptu factory, and an enormous airship held up by zeppelins. He sees Duvall, acting as an overseer of the workmen. Duvall whips one of the men, and is immediately reprimanded by Ra's, who is in command. Ra's gives a speech, saying that he will use the airship, christened "The Phoenix," to destroy the railroad, then move east to Washington and take over the United States government, halting its destruction of the Western environment. Hex is discovered and captured, and brought before Duvall. Hex says that he's there to collect the bounty, and also to pay back an "insult to a lady" friend of Hex's back east. Duvall snorts and orders Hex executed, but Ra's appears and counteracts him again, ordering Hex locked up. As the airship departs, Hex escapes his cell and runs after it, managing to catch a trailing line and climb aboard. At the inauguration ceremony for the railroad, the governor is about to drive the final spike, but a volley of cannonballs from the Phoenix destroys the waiting locomotive and much of the town. As the people scatter, Ra's orders another volley. Hex reveals himself, and pursues Duvall. As he climbs into the ship's rigging, the captain frantically tells his men to stop firing, as the zeppelins holding up the ship are full of hydrogen gas. Hex faces off with Duvall, Duvall wielding a saber, and Hex a bowie knife. In the midst of their furious duel, Hex points a howitzer up toward the zeppelins, and fires, igniting the hydrogen. The ship loses altitude and begins to burn. Ra's escapes the ship in a personal glider, telling the rest of the men to save themselves, but to abandon Duvall. The ship crashes, throwing both Hex and Duvall free. Duvall begs for his life, but Hex tells him he has no interest in killing him – instead, he'll deliver him alive to the law. He finds his hat and remarks ruefully, "I'm gettin' too old for this."
Batman and Robin catch up with Ra's at the airport. now you think it's hex right and Ra's is taking revenge for his foiled plot. But Ra's reveals the man's identity: Duvall, impossibly old and senile.
Ra's explains that Duvall is his son, though Ra's realized early on that he was too cruel and unstable to be his heir. Exposure to the Lazarus Pit as a young man is what explains his longevity – he is now more than 100 years old – but his mind has been shattered by his long prison sentence, and he is now far too feeble for even the Pit to restore him. Ra's had lost track of him until recently. Ra's asks the Dynamic Duo to let him go, so he can do what he can for his son in the little time he has left. Batman agrees, knowing that they will meet again one day.