Firestone
From Tardis Wiki, the free Doctor Who reference
The Firestone was a necklace worn by Lady Clemency Eddison, a gift from her Vespiform lover Christopher. Though she believed it a mere keepsake, the Firestone was actually a powerful telepathic recorder and transmitter. (DW: The Unicorn and the Wasp)
The Firestone was stolen by Robina Redmond, although brought back when the accusations where made.
The Firestone was last seen when Donna Noble throws it into the river, causing the Vespiform to die.
