Tunnel

Tunnel is the thirteenth episode of Season 1, and the thirteenth episode overall.

Synopsis
"As the Nektons explore a mysterious tunnel behind a huge undersea waterfall, strange creatures and strong currents surprise them at every turn. Everything is not as it seems. The true nature of the tunnel will astonish them."

Plot
Beneath the water of a melting ice shelf, the Nektons are in their Knights - Ant in the Shadow Knight with Jeffrey in the Jorange, Fontaine in the Swamp Knight, Kaiko in the White Knight and Will in the Mag Knight - and on the edge of what Will says is the largest waterfall caused by the melting ice flow above. After measuring the strength of the current Ant deploys the Pingers to find what Will believes to be a tunnel behind the falls. Suddenly, a large chunk of ice falls from above and nearly hits Kaiko and Ant who fall over the edge. Unable to hold on, Will and Fontaine are pulled over with them.

After falling for kilometres the Nektons are sucked into the tunnel, Kaiko taking some heavy hits in the process. Using the Mag Knight's spiked feet Will anchors on the tunnel floor and holds everyone else until the current stops. While Kaiko recovers from the hits, Ant finds another Lemurian symbol which is different from the others they've seen. Will matches it and thinks it refers to a name of a pet. Suddenly the current starts up again. Ant and Fontaine grab Will but Kaiko gets sucked further into the tunnel. Ant pursues her and catches up but Kaiko is unresponsive and Ant is forced to stop as she's carried further.

After the current stops Ant notices large creatures called isopods swimming around him. Shortly after Kaiko responds and tells the others she passed out briefly and she's in an area with no mapping data. As Will and Fontaine are about to go further in, Nereus arrives in an old-style diver suit and tells them they must leave immediately. He explains that the tunnel is actually a creature that's asleep and the current is it sucking up food. Meanwhile the White Knight's feet get stuck in some gooey substance rendering Kaiko immobile. Knowing the goo might hold Kaiko against the current (and that trying to break free may wake the creature) Will tells her to stay put. As Ant looks around, the isopods suddenly retreat. Realizing the creature's going to breath again, Nereus directs Will and Fontaine to an adjacent pocket safe from the current. Ant grabs on to a stem but a piece of ice knocks the Jorange off the Shadow Knight and sends Jeffery hurtling through the tunnel.

Nereus explains that he's been at the tunnel before years ago and that the Chronicle of the Deep tells of a group of Lemurian explorers that found the tunnel but accidently woke the creature which they dubbed a monumental a name referring to a whole class of creatures. After putting it back asleep the leader Aloes honored the others by writing about it in the Chronicle and placed a warning at the entrance; the symbol Ant found. Ant finds Jeffery and Kaiko whose CO2 scrubbers were damaged by the current and the goo she's standing in is starting to eat through the White Knight though she is able to break free with the laser.

As the creature groans the isopods attack Ant and Kaiko but retreat after they turn on their lights. Will and Fontaine reach the others and realize that Kaiko doesn't have enough air to get back, however Ant notices one of the Pingers and realizes that since the Aronnax is communicating with them they can control The Rover and get Kaiko out safely. As Will controls the Rover the isopods attack again but are unaffected by the lights and begin sticking themselves to the Knights. This makes Will bash the Rover against the tunnel walls, agitating the creature. When the Rover arrives the White Knight is filled with water and Kaiko is ejected and put in the Rover Ant also ejects from the Shadow Knight to help her. Once in, Fontaine attaches cables to the other Knights and puts Jeffrey in the White Knight. They all start to leave but when they reach the entrance it closes on them. Will uses the Mag Knight's strength to keep it open long enough for the others to escape. Shortly after Will is "burped out".

When they return to the Aronnax they discover the Pingers have mapped out the creature's entire digestive track, revealing it to be many times the size of the Aronnax. Nereus decides to teach Will how to better read ancient Lemurian and explains that there are other Monumentials across the oceans.

Trivia

 * This marks the Mag Knight's first appearance.