Enlightenment

Enlightenment was a prize offered to a group of Eternals by the White Guardian and Black Guardian in a race. The Eternal Captains Wrack, Striker, Critas and their rivals sought the prize in a race across the Sol system. It was claimed to bring anyone's heart's desire to life and Wrack wanted to win so she would never be bored again.

In the end, a share of the prize was awarded to Vislor Turlough by the White Guardian for helping the Fifth Doctor bring Wrack's ship, the Buccaneer, into harbour. Turlough believed it was a huge diamond that he said could buy a galaxy. The Black Guardian offered him the crystal, the TARDIS and anything else he desired in return for the Doctor.

Turlough refused and it was revealed that Enlightenment was in fact the ability to choose between good and evil, concepts of which the Eternals had no knowledge. Turlough threw the diamond at the Black Guardian and upon contact with Enlightenment he was consumed by flames from the blinding light of the prize. (TV: Enlightenment)

In the 27th century, Enlightenment, in the form of the diamond, was offered to Bernice Summerfield by the two Eternals Hardy and Barron. (AUDIO: The Heart's Desire)