Ogami Ittō, the disgraced former shogun's executioner, or Kogi Kaishakunin, is traveling by river on a boat with his young son Daigoro floating behind in the baby cart. A young woman at the front of the boat, clearly distraught for some reason, accidentally drops a bundle into the water, which Daigoro retrieves. Ittō, draws his sword partway and notices in the reflection on the blade that some bamboo reeds are trailing the boat. Ittō is being followed by operatives of his mortal enemy, the Yagyū Clan – a constant threat that he can never ignore. Later, as Daigorou is relieving himself in a bamboo glade, Ittō slices some bamboo stalks, causing some ninja to fall from their perch.
This is a time when there are ronin, samurai who lost their retainership, and watari-kashi, wandering low-class fighters who mostly served for parade, working from one daimyo to the next.
A group of four watari-kashi are idling along the road. Hot and bored, they spy an attractive young woman and her mother being escorted by a servant. Three of them run off to take advantage, but one of the band – Kanbei, the more honorable of the four – remains uninterested. The three knock the escort unconscious and proceed to rape the two women. The servant regains consciousness and is furious when he sees the triad violating his mistresses. He attempts to beat them with his bamboo pole, but is slain by Kanbei, who then also slays the two women to silence them. Kanbei then makes his three companions draw straws, saying the one unfortunate enough to draw the short straw will be killed to take the blame for the rapes and murders.
Ittō happens along this grim scene just as Kanbei is slaying the watari-kashi who drew the short straw. Ittō kills the other two rapists when they attempt to attack him. Kanbei recognizes Ittō and requests a duel. Ittō accepts and they prepare, but at the last second Ittō re-sheathes his sword and calls it a draw, leaving Kanbei to ponder his fate alone. "You are a true warrior," Ittō says, "One I hope lives on." At an inn, it turns out that the young woman from the boat is to be sold into prostitution. Her pimp tries to have his way with her, but she bites off his tongue, spitting the bloody appendage onto the floor. The pimp dies from the injury.
The girl seeks refuge in Ittō's room, who steps in to protect her from the local police. But then the town's real authorities show up – the yakuza, led by a woman named Torizo, from the clan Koshio. After some verbal sparring and defending himself against Torizo's pistol, Ittō agrees to act as a substitute for the young woman and undergo buri-buri (literally "angrily"), a form of torture that involves the subject being hogtied and hung in the air and repeatedly dunked headfirst into a tub of water. The subject is then beaten to unconsciousness by men wielding thick rattan canes and shouting "buri-buri". Ittō endures the torture with his typical stoicism. This frees the young woman from having work as a prostitute.
Ittou, still considered responsible for the death of the pimp, agrees to meet a one-armed man who turns out to be Miura Tatewaki, former first retainer of the Kakegawa clan. Ittou knew him in court: when he had to execute the insane daimyo Kakegawa Ujishige, Miura had to restrain his struggling daimyou, sacrificing his arm to Ittō's killing stroke. Torizo is in fact Miura's own daughter, Miura Tori, who because of the taboo on twins was secretly raised by the Koshio clan. The Miuras want Ittou to kill the man responsible for the fall of their clan as well as 400 other Kakegawa retainers (and for the death of Tori's twin sister): Sawatari Genba, a corrupt officer who sold out the Kakegawa clan to minister Itakura to become governor of the district of Totomi.
Incidentally Sawatari wants to hire Ittou to kill minister Itakura who will be visiting, but Ittou refuses. While giving the slip to Sawatari's men, Ittou is attacked by Yagyuu's ninjas that had been following him. The next day, Ittō has to face the governor's personal bodyguards, one of whom is a sharpshooter and quick-draw artist who wields a pair of revolvers. Through cunning and guile (and the help of his young son Daigorou, who acts as a decoy), Ittō defeats the armed man and takes his guns. The other bodyguard is defeated in a sword duel.
Ittō's battle culminates in his facing the governor's army – perhaps 200 men – singlehandedly. For the first time, the true power of the baby cart is revealed as harbors an entire arsenal of weapons, including spears, daggers, a bullet-proof shield, and a small battery of guns, capable of taking out many enemy soldiers like a heavy machine gun. All of the governor's men are killed as Ittō first takes out half of them with the baby cart's machine gun, and then takes out the rest with his sword and other weapons from the baby cart. The governor is the last to fall when Ittō, deprived of his sword as he falls down an embankment, takes out the pistols he took from the sharpshooter and shoots the governor.
Word of the fight has been passed to neighboring districts, and the ronin Kanbei shows up just after Ittō has slain the governor, and makes his demand again for a duel. Though battle-weary, Ittō accepts the challenge. The fight is over in an instant. Ittō is sliced across his back, but Kanbei is mortally wounded, impaled on Ittō's Dotanuki battle sword.
As Kanbei kneels to the ground, dying, he tells Ittō the story of why he became a ronin – a tale involving an ambush on his master's convoy. Seeing his side outnumbered, Kanbei seized an opportunity and ran ahead to attack the enemy head on. He surprised the enemy and prevailed in deflecting the hostiles, and saved the lord's life as a result, but since he left his lord's side, he was dishonored and expelled from the clan. He questions Ittō whether he had done the wrong thing, and whether being a samurai means to fight and live, or to simply never leave the master's side and die. Ittō replied that he would have done the same. "I am glad to hear that," Kanbei says, who then asks the former shogun's executioner to act as his "second" in the act of seppuku. This Ittō does with honor.
When asked by Kanbei what is the true "Way of the Warrior", Ittō replies that it is neither to simply live nor die, but to live through death. As Ittō walks away and Torizo begins to runs after him, but is stopped by her men. They implore her not to go to him, saying he is not human, but a monster.Tomisaburo Wakayama as Ogami Ittō
Akihiro Tomikawa as Daigoro
Go Kato as Kanbei
Yuko Hamada as Torizo
Isao Yamagata as Sawatari Genba
Lone Wolf and Cub: Baby Cart to Hades was released theatrically in Japan on 2 September 1972 where it was distributed by Toho. An American version was released by Toho International with English subtitles in August 1973. It was later released with an English-language dub by Columbia Pictures under the title Lightning Swords of Death in August 1983.
The film was released to home video in its original Japanese version with English subtitles as Lone Wolf and Cub - Baby Cart to Hades by Samurai Cinema, a division of AnimEigo. An alternate version titled Shogun Assassin 2: Lightning Swords of Death which was closer to the Columbia release was released on home video in 2007.
In a contemporary review, Tony Rayns (Monthly Film Bulletin) stated that the film may resemble an art film to a Western audience where "Misumi and his writer are concerned to revalidate the samurai code every bit as earnestly as movies like Harakiri question it; the result aligns itself directly with those of, say, Mishima's book Sun and Steel." Rayns continued that Misumi's style is "typically Japanese" in its "static, slow, contemplative view of the action, reserving bravua effects for the moments of climax." and that "Though graphic, the violence is not presented exploitatively; any 'kicks' to be hard are confined to the placid close-ups of a severed head or limb, the hideous/magnificent aftermath of violence."