The next full moon is at exam time. Rikki doesn't concentrate on study, wondering only about the cave and crystals, unlike Cleo, whose concentration breaks down when she realizes the moon phase requires the mermaids to hand in their papers five minutes early. The tentacle makes its way to the mermaids earlier than expected, unstoppably, causing weird phenomena. Will has to overthrow the water cooler so the physics exam is cancelled and rescheduled for the next day. Meanwhile in the cave, the tentacle reacts to the crystals by showing a comet's impact, perhaps its own arrival on earth. Unable to stop Zane from intruding on Mako, Will has to follow him; their arrival seems to end the cave show.