An ancient rudimentary time/space device, created by a primitive, clandestine group called the Clocon, from stolen Time Lord Technology, created to be used as a weapon against the Time Lords, who confiscated it.
Constructed in two sections, the Rithe and the Holem, it is mystically attuned to the frequencies of the Time Vortex and Time Lord DNA. With both sections in conjunction, it searches out and imprisons Time Lords by sending out tentacles of meta-genic energy that punch a hole in time/space and grab hold, immobilizing the Time Lords in question. It bombards them with the waves of meta-genic energy, which affects Time Lord physiology, causing death.
The Expirichron components must be connected to work properly. Alone they have separate functions. The Rithe punches the hole in time/space, allowing either the operator or captive to pass through the opening. The Holem, the smaller component, while within the stasis of the Stillness at the center of the Time Vortex, causes cellular mutation, instigating Retrocyclic regeneration. Without both sections being connected, the Expirichron’s time tentacles cannot search out Time Lords with complete accuracy, but only originate a time/space opening in relative proximity to them.
The Holem was removed from the Expirichron prior to its confiscation by the Time Lords and was lost on Gallifrey, becoming a religious relic to a small group of Gallifreyans. It eventually came into the possession of the Soothsayer of the planet Maol. The Rithe crashed with the Clocon ship on the planet Deth and remains in the possession of the Carnage, who have not discovered its purpose.