The Platinum Dragon was trapped by the Doctor thousands of years before the 20th century in the location that would in the future be the Walled City of Kowloon. It would attempt to wake every one hundred eight years, and the Doctor had to return to prevent this.
In 1974, Buddhist monk Hu Cheung was sent to find the Platinum Dragon. He encountered a gang of thugs led by his brother Hu Bak, and he also met the Sixth Doctor and Peri Brown, here to prevent the next waking of the dragon. Bak was absorbed by the dragon, and Cheung defeated it, rescuing his brother. The Doctor trapped the dragon back in its prison for the next hundred and eight years. (PROSE: Exclave)