Scarab (Scarab of Death)

A crystal scarab found in Cairo in 2541 was actually a micro-circuit key to release Horus from the Black Pyramid on Beta Osiris.

The scarab was found by Edwin Carver on a dig in Cairo. It sat in a museum storeroom for twenty years until Carver, plagued by gambling debts, decided to sell it to Anwar Nazir. Before making the exchange, Carver learned the scarab's true purpose and refused to complete the deal. Nazir had him killed but the scarab was recovered by the Fourth Doctor and Sarah Jane Smith.

Captured by Nazir, the Doctor handed over the scarab. When Nazir tried to use it, his body disintegrated, because the Doctor had damaged the scarab. With the scarab now useless, the Doctor decided to keep it in his pocket. (PROSE: Scarab of Death)

When the Seventh Doctor later lost his memory in New York City, he still had the scarab in his pocket. Bart Addison suggested that Silverman use psychometry on the scarab to try and retrieve the Doctor's memories. Silverman told the story of how the scarab came to be in the possesion of the Doctor. (PROSE: Playback)