You have just discovered some buried treasure at the bottom of the sea, and now you have to protect it! You control a diver at the bottom of the screen, and there is a giant octopus and killer shark you need to deal with. Each time an octopus tentacle touches the bottom of the screen, or the shark catches you some of your treasure will be lost. To deal with these creatures, your diver has a harpoon. You need to make sure that you shoot the shark before it can make its way to the bottom of the screen and catch you (the shark will appear again at the top of the screen each time it is shot.) The octopus' tentacles will be reaching downward; each time a tentacle is shot it will retreat back to the top so you need to keep shooting the tentacles before one can reach the bottom. Of course, your diver has a limited air supply. Your companion is in a boat on the surface, and will occasionally drop an air line down. You need to catch this to replenish your air before it runs out (if you run out of air, some treasure will be lost). The game ends when you have lost all of your treasure.
The gameplay is fast-paced and challenging. You must manage your air supply while avoiding the shark and octopus's tentacles. You need to time your harpoon shots carefully to deal with both creatures effectively. As you progress through the levels, the difficulty increases, with more frequent appearances of the shark and more aggressive octopus attacks.