_CAPSULE SUMMARY:_
Tommy, Adam, and Rocky are training for a charity karate competition, benefitting the Angel Grove Children's Home. Tanya & Kat have been spending time with the kids from said place, and have befriended a young pre-teen boy named Justin Stewart. His father works in another town, and dumped the boy off at the shelter. Anyway, during training for the event, Rocky screws up a kick, and goes flying, slamming onto the cement on his back. He ends up in the hospital with a serious spinal injury (well, maybe not his spine, and maybe not too serious, but he ends up in traction).
Divatox, an evil space pirate, and her crew of alien space pirates (including her nephew Elgar, and first ship-mate Rygog), chase a small alien wizard named Lerigot from his home on the planet Liaria. He comes to Earth, seeking Zordon for help. Divatox wants his key, and its ability to open intergalactic portals and such, to free her fiancee, an ultra powerful demon master known as Maligore. She follows him to Earth in her Subcraft, which, as per its name, is a submarine and space craft. While landing in Angel Grove Lake, Bulk & Skull (now Junior Police Officers again) are abducted on their way to relieve Lt Stone of duty for the night, simply because they spot the Subcraft landing. They're brainwashed, which turns their hair white, and makes them talk in odd languages, while acting even odder than their usual selves.
The Power Chamber has gone an overhaul of its design, without any reason why. It barely even looks like the same place, much brighter in color, with the glass cases on the far wall no longer featuring old Ranger costumes, but merely the current Rangers' colors. Alpha 5, also, has a new body, with no explaining. Well, Tommy & Kat are sent into the rain forest of South America to search for Lerigot when he lands there. The hazards of the jungle are nearly as bad as Divatox's Pirhana Warriors (or whatever they're called). Kat plummets over a cliff, and despite morphing into Zeo Ranger 1, Pink, briefly, still gets a bad gash in her leg when hitting the river below. They find Lerigot, who is able to heal her wound, before they teleport him back to the PC (new teleportation effects for everyone, by the way).
Jason & Kimberly are in town, planning to surprise their old Power Teen pals. But, first, are going for a brief scuba exkermish. While doing so, they get kidnapped by Divatox and her crew, and held for ransom of Lerigot. But, being evil, Diva & Co. don't follow through, and end up taking the little munchkin creature without forking over Kim & Jason. She needs them for human sacrifices! The Subcraft is heading to the Nemesis Triangle, where within, on the island of Muiranthias, Maligore can be found, mystically bound into the volcano there. Lerigot opens up the entrance to the Triangle (being threatened with death doesn't phase the little guy, but Divatox also has his wife, Yara, and new baby, Bethel, held as well, so he's forced to do the evil bidding), but the Rangers are unable to enter as easily. They give up their Zeo Powers (without any real explaination why), and given new Turbo Powers, each Ranger getting a key, based off Lerigot's technology, and powered by Zordon's planet of Eltar, it seems. These powers work with the newly built Turbozords, each of which doubles as a car! Tommy gets the Red Lightning (a sports car), Adam the Desert Thunder (a van), Tanya gets Dune Star (a dune buggy style vehicle), and Katherine receives Wind Chaser (a car). With Rocky laid up in the hospital, a new Blue Ranger is chosen. Who gets to be it? Someone qualified? Like, perhaps, a former Ranger? Nah. When the Ranger Teens visited Rocky in the hospital, Justin overheard them talking to Zordon & teleporting, so he ends up, mostly due to his expert martial arts skills, getting the nod from the neck-brace-wearing Rocky for temporary replacement. Seems when Justin morphs, his body grows and fills out to fit the size of a stuntman. He pilots the Mountain Blaster, a truck or SUV.
There's a brief cameo by Rita Repulsa & Lord Zedd, when Divatox calls her old "pal" Rita up, asking for advice on defeating the Power Rangers. Rita more or less laughs at her for having to deal with the Rangers, aware she'll fail just like she herself did. Zedd's sole line is that of his snoring, sleeping at the time, wherever the heck it is he and Rita are living. Don't look for any clues as to continuity to Zeo here, folks!
So, the four teens, and their new preteen teammate, board an ancient ship called the Ghost Galleon, and use their Turbo Keys to power it up. It'll provide entrance to the Nemesis Triangle, and allow them to bring their new Turbozords with 'em. There's a whole subplot of how Kim, Bulk & Skull escape from the Subcraft, and end up caught by the native inhabitants of Muiranthias. But since the Muiranthians end up doing Divatox's bidding anyway, it's pretty much a waste of time to talk about. So, Divatox & company get to the temple of the volcano first, and prepare to sacrifice Jason & Kim in an attempt to free Maligore from his 5000 year imprisonment. But, the Turbo Rangers burst in and interrupt the ceremony. Jason & Kim are turned evil by the volcano, and help those nutty Muiranthians fight the Turbo Rangers. Plenty of inner angst is dredged up by evil Jason, who vents a lot of jealousy over Tommy when fighting Red Turbo Ranger. Evil-ized Kimberly, as well, when she takes on Pink Turbo Ranger. But luckily, Lerigot's spells and such cure the two teens of their evilness soon enough, and they help their old teammates in battle, despite their lacking powers.
Still in need of a sacrifice, Divatox knocks Elgar into the volcano (don't worry, as you'll see in "Shift Into Turbo, Part I", he's merely singed). Maligore arises from the lava, and the Turbo Megazord is formed to defeat him (the Turbozords grow from normal vehicle size to giant Zords). With the use of its Turbo Saber, Maligore is knocked over the side of the island, into the untamed waters below. Given how Maligore is pretty much implied to be a demon, such a thing is lethal to him, and he explodes entirely upon hitting the waves (what, you think he was imprisoned on an island for the VIEW?). Divatox, though surprised to see the man she was to marry was a hugh, 50 foot hulking monster made of lava, and even turned off by his looks, vows to gain revenge on the Turbo Rangers for killing her fiancee. (well, sort of, she doesn't exactly vow that here, merely retreating with Rygog to the Subcraft once Maligore and the Megazord do battle)
It all ends with Tommy, Adam, and Jason fighting a Stone Canyon team of martial artists in the arena for the charity of the Little Angels' Orphanage or whatever the heck it was. Rocky's out of the hospital, but his back is still sore. Ernie appears in the audience briefly, in his last onscreen appearance. Bulk & Skull (after finally getting a chance to muck around in the Megazord cockpit during a cut scene shown during the end credits) are returned to Angel Grove safely, their minds more or less no worse for wear. Lerigot, his wife Yara, and baby Bethel, are safely returned home offscreen.
Go buy the movie if you want to know more. It's available on VHS, DVD (double sided disc with MMPR:TM), and single-movie DVD (neither are special editions).