The Quevvils were a race of porcupine-like aliens, native to the planet Toop, who have been at war with the Mantodeans, huge alien insects resembling preying mantises, for reasons that have never been determined. Unfortunately, this conflict was an ultimately self-defeating struggle, as neither side could actually successfully hurt the other; the Mantodeans couldn’t hurt the Quevvils as they could just curl up and escape any attacks from the Mantodeans, and the Mantodeans’ armour prevented the Quevvils from hurting them with their porcupine-like spines. Another problem lay in the fact that the Mantodean stronghold was surrounded by a forcefield keyed to Mantodean biology, and they were also riddled with traps to deter anyone trying to enter.
With these factors driving them, the Quevvils eventually travelled to Earth, where they handed out the computer game Death to Mantodeans – a game based on the conflict going on back home, practically giving The Doctor their plans thanks to the pre-game introduction – while subsequently setting up fake ‘lotteries’ for holidays. Anyone winning the holidays was taken to the Quevvil homeworld and implanted with a remote control device that ‘wired them up’ to a copy of the game. Armed with a disruptor to shut down Mantodean technology, the humans were sent into the fortress, where those playing the game back on Earth could use them as ‘players’ to approach the centre of the Mantodean fortress and disable the forcefield with the disruptor… little realising that, when they were ‘killed’ in the game, people actually died on the Quevvil homeworld as the ‘players’ were eliminated. As the game was played, the Quevvils monitored the scores, waiting for the player who would be able to guide them through the fortress and win the ‘game’.
This objective was eventually fulfilled when the Ninth Doctor and Rose Tyler, while paying a visit to Rose’s mother, dropped in on Mickey Smith, The Doctor subsequently having a quick play on Death to Mantodeans and getting a new high score in a matter of moments. Initially the Quevvils captured Mickey by mistake, but The Doctor managed to get himself captured by getting another new high score, he and Rose being taken to the Queevil’s homeworld as Mickey managed to escape.
With The Doctor now forced to play the game with Rose as his ‘carrier’, he managed to rewire the control console to allow Rose to use her ‘superphone’ to call Mickey back on Earth (Albeit with The Doctor talking through Rose rather than Rose talking herself), thus encouraging Mickey to find anyone with saved games and work to protect the innocent humans trapped there from the Quevvils and the Mantodeans. Having disabled the feature on the control devices that prevented the players form meeting (Thus resulting in the truth about the ‘carriers’ being revealed), The Doctor was able to shut down the devices using the sonic screwdriver (Which he’d given to Rose before she went into the fortress), although some humans were still left in the fortress.
Eventually, The Doctor managed to navigate Rose to the centre of the Mantodean fortress, where she used her disruptor to shut down the force field. Instantly the Quevvils teleported into the fortress, but realised too late that The Doctor had tricked them. while The Doctor distracted the Quevvils, Mickey and his friends had moved their respective players right up to the control room, and, using split-second timing, used their disruptors to shut down the Quevvil teleporters mid-teleport, after the Quevvils had been disintegrated but before they were put back together. Having removed the control devices and destroyed the Quevvil teleportation devices so that the survivors couldn’t try something like that again, The Doctor and Rose then departed, The Doctor wishing to leave promptly to avoid admitting that Mickey had done a good job.