You're lost in a treacherous underground cave system and, seeing as the Thunderbirds are busy starring in a game of their own, it looks as though you're gonna have to find your own way out.
If you think that's easy, think again. Before the exit to each of the sixteen caves unlock, ten diamonds must be collected. And out to stop you is a gang of Nomad guardians, baying for blood and not happy at you being there.
Lost Caves is a straightforward Boulderdash clone, nothing more, nothing less. Games such as this used to be classic budget fodder but, with the much more playable Boulderdash I and II both available at the same price as this, you're better off going for the originals.