Trave's TARDIS

A future incarnation of Trave travelled back in his own personal history in an unregistered TARDIS to prevent Rassilon from gaining too much power on Gallifrey after seeing the results in the future.

When the TARDIS materialised, this future version of Trave was immediately challenged by a member of the Chancellery Guard, whom Trave shot. The TARDIS was then subject to forensic examination. According to Castellan Bovari, the TARDIS had no serial number and features they didn't immediately recognise. The future Trave destroyed the navigational circuits to prevent the Time Lords of the time from determining how far into their future they'd come.

Romana and Livia both suspected the Time Lord operator was trying to change history and the outcome of the Time War. (AUDIO: Havoc)