This begins with Tarzan hunting a deer in England, armed with only a knife. He's sent an invitation to hunt with Lord Marchmain--and he accepts. However, they want him to use a rifle--and not having any experience he's a terrible shot. The English hunters mock him, saying it's hard to believe he's a big game hunter in Africa. One of them tells him that if he hits something they'll give him a banana. Jane is furious. This is interrupted by some nearby cries, which turns out to be a poacher caught in a trap. Lord Marchmain doesn't want to help the man and forces him to crawl, which infuriates Tarzan. When they start shooting at the crippled man he attacks them--then they start firing at him and Jane. Little do they know that these guys are really disguised Therns from Mars. Tarzan and Jane run and take cover in a nearby cave entrance, which turns out to be an old mine. They follow the tracks--and enter a gateway that leads to Barsoom (Edgar Rice Burrough's Mars) and find themselves in the ruins of a city. There's a blonde-haired, white skinned boy being pursued by red Martians and so Tarzan intervenes. The boy, who is a Thern, explains how John Carter, also from Earth, is a brutal dictator. The boy takes them to his city, where they meet the obese ruler, who is also the boy's father.
John Carter is captured by the Therns and is put in the arena, where Tarzan is supposed to fight him. But Tarzan begins to think that his benefactors have been lying to him, which they have. Now, they are holding Jane hostage and threaten to harm her unless he does battle with the Warlord of Mars. However, Jane easily escapes because in the lower gravity of Mars she's much stronger--and leaps away. Pissed, the Thern ruler releases a dozen white apes--and the two heroes must work together to survive.
I liked this far better than the Tarzan-John Carter Warlords of Mars series from 1996, though I didn't like that Tarzan is portrayed as feeling insecure about "fitting in" and "being a freak". As Sara Silverman would say, this just makes him seem like a "Puthy". If there's one thing that Tarzan is not is insecure. Still, if you're a fan of Edgar Rice Burroughs you'll enjoy this graphic novel.