Underworld

You have been stranded on the island of Brannal. The only way for you to escape is to collect the five Keys of Time and take them to the Keeper of Time who will enable you to escape. The only problem is that the Keys are in the possession of the Dark Lord and his followers who rule the island, and naturally they're none too keen on letting you get away.

Authorship is unclear, since according to World of Spectrum, it was published in 1985 by Kevin Rae, but also published in 1986 as a type-in listing in ZX Computing magazine, credited to David Naylor.