These spoilers are from a script review by LatinoReview.com:
We open on JONAH HEX bringing a few ne’er-do-wells to the town of Stunk Crick to collect on a bounty. But things don’t work out as expected and there’s a large shoot-out. I’ll give you one guess who walks out in one piece. The encounter does not bode well for Jonah and he gets his ugly mug on a wanted poster with a hefty sum attached.
Meanwhile, a group of ruffians led by the baddest madman of the West, QUENTIN TURNBULL, blow up a train full of soldiers, women, and children. They make off with the train’s contents, most of which happen to be munitions for the recently-successful Union army.
Later on, Jonah visits LEILA, a lovely raven-haired lady of the night who happens to have a thing for him. As Jonah’s enjoying himself, a troop of government militia, led by LIEUTENANT GRASS, rides into town searching for the bounty hunter.
Jonah gets word of this and races out of town like a bat out of hell; but after a long chase, he is cornered by the men. Jonah tells them to get on with shooting him, but Grass laughs, saying that they aren’t there to arrest him, they’re there to employ him as a bounty hunter. The target? Quentin Turnbull.
Grass says Jonah is perfect for the job – not just because his reputation as a tracker precedes him, but also because of his history with Turnbull, a history in which Jonah is responsible for death of Turnbull’s son, and, based on Jonah’s reaction, probably much more. In response, Jonah now laughs, saying that Turnbull killed himself after the war. Grass tells him that Turnbull is very much alive and a huge threat to the recently restored Republic. Hex quickly agrees and sets off in search of Turnbull.
En route, Jonah has to drudge up his dark and haunted past to try to locate Turnbull and uncover his plan, but those familiar with Jonah aren’t exactly happy to see him when he comes around. And even though he does have allies in his quest, that price on his head can be pretty tempting, as can the desire for revenge