The Kartz-Reimer module was a prototype time machine invented by the Third Zone scientists Kartz and Reimer.
Under the direction of head of projects Dastari, Kartz and Reimer had been conducting experiments in time travel aboard Space Station Chimera, finally building a primitive time capsule called the Kartz-Reimer module. Their work was advanced, but the final secret to making the machine function eluded them. The Kartz-Reimer experiments had begun to affect the space-time continuum which attracted the attention of the Time Lords, who sent the Second Doctor to advise the scientists to halt their experiments to avoid further damaging the continuum. Dastari, his Androgum servants Chessene and Shockeye, and the Sontarans Stike and Varl with whom they were secretly working murdered everyone aboard the station apart from the Doctor's companion Jamie, who escaped into the station's substructure. They falsified evidence implicating the Time Lords in the attack and abducted the Doctor to Earth, bringing the Kartz-Reimer module with them, in order to extract the final secrets of time travel and get the module working.
The abduction of the Second Doctor was psychically felt by the Sixth, who went to Chimera and found Jamie among the wreckage. The Sixth Doctor, Peri Brown, and Jamie travelled to Dastari and the Sontarans' base in an old hacienda outside Seville, Spain to rescue the Second Doctor, and in the course of events the Sixth Doctor and Jamie encountered the Kartz-Reimer module in the hacienda's cellar. The Doctor marvelled at how close the module was to a working time machine. Aware that Stike was covertly listening, the Sixth Doctor explained to Jamie that the machine would never function without a Time Lord taking the first trip, priming it with the Rassilon Imprimatur. Stike then revealed himself and forced the Doctor into the module to prime it; the Doctor took the opportunity to sabotage the module by paring the interface of the briode nebuliser, leaving a thin membrane so it would only work once more. Afterward, Stike forced Peri to take a trip in the module to demonstrate its functionality. Satisfied by Peri's safe return that the module was now fully functional, Dastari, the Androgums, and the Sontarans moved forward in their various plans.
Later, after the deaths of Dastari, Shockeye, and the Sontarans, Chessene attempted to use the Kartz-Reimer module to escape. The Doctor's earlier sabotage took effect and the module exploded, killing Chessene. (DW: The Two Doctors)