Follow the creature.

Whatever shook the sub zoomed off to the left, so your best bet is to turn that way. The wake left by it must have left a trail of disturbed sand.

You sit back down in the pilot's seat and steer the sub to look to the left. The creature was waiting for you to do something. The tail of the creature was in the headlights for a fraction of a second before it took off straight ahead. You give the sub a little gas and the propel the sub forward. Again, the tail was in your view just long enough to see it before advancing further.

Strange. You've never seen anything act like this before. Anytime you find an aquatic fish, it took off and kept going until there is was gone for good. This creature seems to be leading you somewhere. Whenever it signaled for you to turn, you would zoom left or right over the head lights. If it wasn't for your GPS unit tracing your path, you'd assume it was a fish leading you in circles, but the path was more or less a straight line.

After several minutes of this, two human hands slammed against your view port. Your heart jumped into your throat and you slam on the breaks. The hands push off and you notice that you're face to face with some kind of structure made out of various shipwrecks. Still though, the hands pushing porthole do freak you out.

The hands push off the glass and you catch another glimpse of the creature. This time your certain that you did see a human-fish hybrid and that there must be funny stuff in the air because that makes no sense.

LSD in the air does, however, make more sense than what decided to press itself against the window though. The human-fish hybrid pressed its torso against the glass. From what you could tell, it was a well endowed woman showcasing her sexy assets. Her smile was sweet and innocent as her long hair floated in the water. She kissed the glass and swam up to the top of the sub. She left an imprint of her lips and breasts behind.

You could hear knocking again. This time, it was against the hatch leading to the outside. You'd need to wear your pressure dive suit before you head out obviously.