On a luxury cruise ship, the Argonautica, something hits the ship and attacks the crew and the passengers. Meanwhile Treat Williams and his crew are taking a bunch of mercenaries out into the middle of the ocean to an undisclosed location.
Williams and the mercs discover the ship at which point the mercs reveal they were hired to rob the ship and the passengers. They board the ship looking for the vault.
Meanwhile Williams and his crew try to find parts to repair their ship which was damaged by a loose boat from the cruise ship. Both parties are attacked by the creatures which look like weird tentacle monsters.
They find survivors including thief Famke Janssen and the owner of the cruise ship who actually hired the mercenaries to rob his own unprofitable cruise ship.
Like I said the movie is stupid but entertaining and writer director Stephen Sommers would go on to direct the reboot of The Mummy to greater success.