The ship.

You decide to investigate the ship. It might not lead you to the city of Atlantis, but it's better to bring something back up with you than nothing.

You head on over to the wreck and search it for any form of identification. Circling the hull, you managed to find some letters painted onto the wood. Unfortunately, some of the paint wore off or is hidden from your sight by barnacles. Your best guess is that this is the name of the ship is The Massachusetts. It can't be that old since the state has existed for quite some time. Nevertheless, you continue looking it over to find something valuable to bring up.

As you round the wrecked ship, you note that there is an opening the in hull that you could sneak into with your pressure dive suit since the opening was too small for the whole submarine.

As you record your findings in your log book, you here a rapping on the sub's hull. Probably some deep sea fish checking you out, but you notice a sort of pattern to the knocking. One tap, followed by two quick taps, then three, five, seven, and repeat. Those are the first five prime numbers. Something like that should only happen by coincidence once, not three or four times since you noticed.

You stand up from the pilot's seat and walk to where the rapping was coming from. You managed to track down where it was coming from, but there were no portholes available to look out and see who or what was signaling you.

You knock back "Shave and a Haircut" and the mysterious rapping stopped. You've either scared whatever was out there or let it know that you were in there. It's just something else to write in your log and you head back to the pilot's chair.

One your way, a creature zooms past your headlights. The wake of whatever that was rocked the sub and throws you off balance. You brace yourself with the wall as your heart starts to pound out of your chest. You try to rationalize what just happened but you can't ignore that the creature that frightened you had the body of a human and the tail of a fish.