Confession Dial
A confession dial was a small, circular disk containing the last will and testament of a Time Lord. According to ancient Gallifreyan tradition, it was to be delivered to their closest friend on the eve of their final day. (TV: The Magician's Apprentice)
After being summoned by Davros, the Twelfth Doctor left a confession dial with Ohila for her to deliver to Missy. (WC: Prologue) Missy brought it to Earth and met with Clara Oswald, and explained that the confession dial was to be given to a Time Lord's best friend prior to their death. Clara attempted to pick the dial up, believing that it was intended for her, but it responded by shocking her. Missy explained the confession was for herself, and would only open after the Doctor died. She took it with her to Essex in 1138 and to Skaro. (TV: The Magician's Apprentice)
After the Doctor, Clara and Missy were captured by Davros and the Daleks, Davros came into possession of the confession dial and the Doctor's sonic sunglasses. When the Dalek city was destroyed by an overuse of regeneration energy, the Doctor stole back the confession dial and pocketed it, not intending to use it for a long time. (TV: The Witch's Familiar)
