Nappa awakens in the place where he died; he reflects on how he was badly defeated in combat, then betrayed and killed at the hands of a prince he served loyally for so many years. He thinks at first of resuming his rampage across the Earth, but before he can act on these thoughts, he feels something strange, and heads towards this strange eminating sensation. It's later he realizes that he can now feel power levels, and that what he was feeling was the Namekians and Z Warriors being teleported to Earth. He realizes that Vegeta, as well as some of the warriors he fought before he died (Piccolo, and Gohan), are on the same planet as himself; and it is obvious to him that they are way, way more powerful than him. Nappa panics, and flies away in fear... then spends the next several weeks in hiding on this strange planet.
Nappa's Return Saga
Months later, on Kami's Lookout, Garlic Jr has returned with his Spice Boys, and, after a one sided fight, manage to trap Kami and Popo in a bottle. He announces his intent to find the Black Water Mist and release it upon the Earth... when he is interrupted by a large bald man, carrying a woman and a small wrinkled person, crash landing on the lookout. After a few moments, he recognizes one these figures as Nappa, the Saiyan who threatened Earth a few months prior, while the tiny figure introduces himself as Emperor Pilaf, "the new ruler of this world". The third is introduced as his henchwoman, Mai.
The two diminuative would be tyrants get into an argument, when Nappa makes a suggestion that Pilaf's strongest fighter (himself) takes on Garlic's strongest henchman at the base of the tower; Spice laughs at this, and volunteers. While the duel is set up below, Pilaf learns that this pointy eared adversary is not Kami; as he hears Garlic Jr describe himself, the would be Emperor starts to get cold feet. On the ground, the demon taunts the alien pointing out that he's several times stronger; Nappa smiles and says, "yes.. a few times stronger, that's true" while looking up. It's then that Spice notices that the alien has created an artifical moon, and sees his adversary turn into a giant monkey, more powerful than himself.
As Nappa powers up into Ozaru form, the Z Fighters feel an energy burst the world over - but only Tienshinhan and Piccolo instantly recognize him as the Saiyan they had fought months before, and so they instantly begin flying toward the power up. (Krillin, Gohan, and Yamcha - who didn't die at the Saiyan's hands - hold off on acting until they can figure out what they're dealing with as a result, and as a result they they don't arrive at the Lookout until well after the action has played itself out.)
As events unfold, we learn via flashbacks how Pilaf Crew got this strange crew together: After hiding out from the Z Fighters for sometime, Nappa became despondent and fell into alcoholism, showing up at drinking establishments, sucking their stock dry, and basically being a super-powered nuisance. Pilaf hears about this and sends Mai to attempt to seduce him and bring him into their organization; at first she objects to such a mission, but is overruled in the usual slapstick manner.
Nappa is at first cold to Mai's transparently false attempts at romancing him, but eventually starts to bond with this woman whose loyalty to this Pilaf person can't help but impress him; he eventually decides to join this army, mostly out of pangs of nostalgia for his own lost band of Saiyan brothers. The new alliance is not without its tension - for example, Nappa takes issue with one of Shu's goofier moments, saying that such behavior would get a man killed on sight in any self-respecting Saiyan company. Shu is so spooked by this he finally breaks from Pilaf running, never to return. Pilaf is at first miffed at losing a minion, but Nappa promises to make it back by becoming stronger than ever; cue the training montage.
Back in the present, Ozaru Nappa is holding his own against Spice, but both combatants are wearing themselves down. As the battle drags on below, Tien and Chaotzu are the first Z Fighters to show up at the Lookout, and begin trading blows with lesser members of the Spice Boys; Tien manages to badly damage one with a kiko-ho or two, but also wears himself down. Frustrated with the delays, Garlic lashes out in anger and easily kills Pilaf. As Tien and Chaotzu are about to fall to the remaining adversaries, Piccolo shows up, and kicks Garlic off the lookout entirely, then finishes off the remaining minions. Meanwhile, Garlic Jr lands ignobally at the base of Korin Tower, and becomes enraged that things went so wrong. He gigantifies, even moreso than he did in Dead Zone, to the point that he's about half the size of Ozaru Nappa... but also far more powerful, as he demonstrates by proceding to mercilessly beat on the Saiyan (killing Spice with a stray ki blast). During all of this fighting, Mai makes her way to the bottle holding Kami and Popo and frees them.
Once the lookout is cleared, she looks down to the earth... and sees Ozaru Nappa losing badly to the enlarged Garlic. She implores the Namekian to intervene and save her comrade.
PICCOLO: And why would I help you? You just tried to take over the world…
MAI: You... how dare you! It's no worse than what you've done, and damn well know it!
KAMI: (steps in, chuckling) She has you there, Piccolo.
And so Piccolo, groaning, flies down to the earth, where Garlic is crushing the now reverted Nappa; he knocks the villain out, and starts badly beating Jr in the ensuing fight. Desperate, Garlic summons the Dead Zone, and… well, you know how that goes.
Just as Garlic falls into his own trap, Gohan, Krillin, and Yamcha land next to Piccolo and a fallen Nappa. Tien flies Mai down from the Lookout, and she runs to Nappa's dying body. She demands they give him a sensu to heal his injuries, but the Z Warriors hesitate. Piccolo tries to get Nappa to first promise not to try any of this conquer/destroy the earth crap any more... only for said Saiyan, dying as he is, to refuse, saying that he will not abandon his comrade. "I wanted to die... as a warrior... with a cause... with comrades... and now I can..." At this, Mai openly cries and begs Nappa not to die on her account; she promises on his behest.
The fighters look at each other, save Gohan, who steps forward and feeds Nappa a sensu bean. The bald saiyan swallows the gift, surprised by the boy's mercy; Piccolo tells him "Don't make us regret this".
Sometime later, when they're alone, Nappa laughs and informs Mai of "the joke": with his latest Zenkai bonus, combined with his Ozaru form, he is now strong enough to take on any of the Z Warriors left on earth, including Gohan or Piccolo, and will still gladly help her take over the world... if she still wants to. Mai, at a loss for words, can only say she'd need to think about it; considering, she considers that even if she said yes, it would take weeks of planning to pull something like this off.
Weeks later, with the partners yet to make their next move, Nappa, and several of the Z Warriors, feel an all too familiar and terrifying power level making its way to Earth...