The party meets Ninth Truth at the access outpost and are tasked with heading through the underground tunnels to the Saltsea, where they are to take a recently constructed submarine and use it to reach some tunnels only accessible from underwater. These tunnels have never been explored before, and might contain new sources of food. Ninth Truth is concerned that system-wide trade, on which Kylal is heavily dependent for imports, will be disrupted by the recent failure of the Orion Gate, and so sees obtaining new food supplies as a top priority.
As the primary elevator is closed for maintenance, the party head across the ice to the auxiliary elevator, fighting a pack of Ice Beetles along the way. They then descend into the tunnels, fighting past Cavern Worms and Rock Beetles, to reach the shore of the Saltsea - a vast body of dense brine.
Among the outposts and workshops on the shore, the party track down the engineer behind the submarine, who briefs them on its operation as well as the location of the tunnels they are to explore. The party are directed to obtain a sampling device from another engineer, which they will need to record and analyse any food sources they find. After figuring out where a local child had hidden the payment for said device, the party obtain this. They also persuade Zeitgeist to provide funding to rent some protective sentry turrets. With the supplies gathered, the party set out into the Saltsea, with Gathering Flow at the helm of the submarine.
The first underwater tunnel leads to an opening where the party park the submarine and proceed on foot. They come upon several species of plant, including one that they get repeatedly entangled in and another that is highly acidic, both of which they take samples of. The multitude of less dangerous plants present are being tended to by Honey Beetle worker drones, one of which the party kills and also samples (as well as taking a small sample of honey that it had exuded). Genuine Article preserves the Honey Beetle remains to pick up later.
Further along the tunnel, the party find themselves at the edge of an immense cavern, filled with hundreds of thousands of Honey Beetles of numerous sizes - this is the Honey Beetle Nest. The party attempts to take a proper sample from a nearby pool of honey, but are fought back by Honey Beetle soldiers and workers, and are forced to retreat with an incomplete sample. Budding Leaf manages to salvage the honey sample, but damages the sampler in the process, reducing its speed of operation. The party retreat back to the submarine (and Genuine Article retrieves her Honey Beetle carcass).
The party proceed to the second tunnel. After fighting past a voracious slime creature, they find themselves in a cavern containing numerous species of mushroom. These fungi are home to developing Cavern Worm young, which do not like being disturbed by the party trying to sample the mushrooms. Despite the onslaught of tiny worms, the party are able to sample most of the mushrooms. Genuine Article is also able to extract some poison from one of the mushrooms and turn it to a combat purpose.
The party return to the submarine and head for the third tunnel. They once again park the submarine in an opening, and Gathering Flow observes that they are right on the edge of the Kylal Ship Heart's protective range. While reticent to head further into the tunnel and into Decay, the party's curiosity is piqued by the strange shape of the tunnel: rather than being naturally formed like the others, it is an upside-down pentagonal prism, with smooth walls (albeit covered in the bioluminescent plant-life common throughout Kylal's tunnels). Leaving the turrets set up to guard the ship as previously, the party venture into the tunnel and the Decay.
A short way down the tunnel, the party are hit by a debilitating pulse of energy that drains their equipment - and also drains the light from the bioluminescent plants, plunging them into darkness! Their energy and the light recovers, but in the darkness, Dread Moles have emerged. They may not be Decay creatures, but they are certainly vicious. The fight is tough with the lights intermittently dropping out amid Decay pulses, but by leading the moles into the turrets the party are able to survive, and head further down the strange tunnel.
The tunnel opens out into a medium-sized chamber that may once have had similar pentagonal patterns, though has now mostly collapsed - a rock-fall prevents any further travel. In the middle of the chamber, on a ruined pedestal, sits a large orb: perfectly spherical, and seemingly made entirely of rust. The party debate what to do and whether they should just leave, but Genuine Article thinks the orb might be valuable, and reaches out to touch it.
At the slightest contact, the orb immediately disintegrates into a thick cloud of rust particles, and Decay creatures arise from the rubble of the room, among them a lumbering creature that intermittently pulses restorative forces at the other Decay creatures. The party beat a hasty retreat to the submarine, successfully recovering one of the turrets (while the other is destroyed by the Decay creatures), and head back the way they came.
The party return through the Saltsea to the shore encampment.