Kei blasts the drowned blade into two pieces. It tries to reassemble: DC13 CON Save: 19

But he blasts it again – DC14 CON Save: 18 – and again – DC20 Con Save:  15

...until it is finally still. Combat is over. The rotting sea chest and the pulsing rift in the sea floor are now unguarded.

Gerrard:

Drifting back from the combat finale, Gerrard feels the start of a new ailment add to his already-cursed slimy skin.  Sighing, he asks, “Any more healing where that came from?  I barely survived that fight,” as he picks up his dagger and goes to cautiously check the chest for traps before preparing to open it with the tip of his rapier.

Perception: 15

Kellen

Kellen swims over to Gerrard, shaking his head. You know, before I met you guys, what...2 days ago? I barely went underwater if I could help it. Hold still. Kellen once again concentrates on the mandolin, placing a hand on Gerrard's shoulder. It's a lot easier to cast this stuff when I can actually play the mandolin, too.  Warm energy rushes from the glowing mandolin, through Kellen's arm, and into Gerrard.

Cure Wounds: 20

Kellen

Cursing under his breath, Kellen preps another spell. See? That wasn't nearly as powerful as it should've been. Here, close your eyes...let the warmth embrace you. Once again, Kellen's words wrap around Gerrard, momentarily fighting the chill of the icy water.

Healing Word: 28

Kei 

Kei reaches into his sack as he walks towards Gerrard and pulls out one of the strong healing potions given them by the Captain. "Tough fight, you need one?" He casually hands the potion to Gerrard if required or stashes it again as he heads to the glowing hollow. He peers in.

Perception 22

Gerrard:

     “Thank you both,” says Gerrard, taking the offered healing potion and drinking it.  He also checks the corpse of the captain for anything of use (and maybe checks out the sword he was using too) after he opens the sea chest.

Greater Healing:  16

Kei looks into the funnel-shaped hollow, some three feet in diameter, in the cavern floor. There's fresh digging around it. The hollow descends about two feet and terminates in a narrow, one-inch-wide hole into the bedrock below. The pulsing light emanates from this hole. The narrow opening continues down as far as you can see. The eerie, many-colored light, composed of unnatural colors, pulses erratically. It gives you an uneasy, unhealthy feeling to look into. This is the source of something broken, something unnatural, something evil.

Gerrard finds that the rotting sea chest is full of coins (5,000 sp, 1,850 gp, and 75 pp, if you're counting) and ten masterfully cut pieces of jade depicting various sea animals (and certainly of significant monetary value.) It feels like an offering.

Kellen

Kellen sees inside the chest as Gerrard opens it up. Holy-this is enough to set us up for a very long time, my friends. Then he notices Kei floating closer to the light, and, curious, swims after him. Feeling the eerie feeling as he gets closer, he tries to identify what's causing it.

Arcana 11

Stealth (for getting up close and peering into the opening) 24

Gerrard:

Grunting in agreement as he lifts the chest, Gerrard takes it to the diving bell and secures it inside, as he can think of no easier way to get it to the surface eventually.  

While he is over there, he gives the signal for “okay” and “hold position” as a way to reassure the crew.

Kellen senses this is an unnatural rift between worlds, a tear in reality, a portal to a place of alien horror. This is an unholy wound. It oozes with necrotic energy. And who or whatever recently excavated it was a pawn to its power.

The crew in the ship above returns a signal of acknowledgment to Gerrard.

Kei 

"What could've made this split? The ground I understand, it could simply have been these skeletons. But the tear? That is a little unnerving." Even Kellen, who has known him the shortest, can tell this situation has sparked fear in Kei.

Gerrard:

"I have no idea," says Gerrard, "But you are right--something feels very wrong here.  Do you have any idea how we can seal it off, maybe sever its connection to the surface world?"

Kellen

It feels...unnatural...like those things that enslaved me for so long. Kellen shudders. I don't know if we can seal it...but I guess we can try. Kellen hold out the mandolin, once again glowing with energy. The energy forms into a beam, aiming directly at the center of the tear, as Kellen tries to close it.

Kei 

While Kellen plays his tune, trying to close the rift, Kei wracks his brain trying to think through the broken memories of his time in the Shadowfell, looking for anything ha might help them.

Arcana 17

Kellen focuses his power on the rift, but its power is substantial. (Kellen: Make a DC19 Charisma check.)

Kei can feel the interplanar nature of this rift. But whatever is on the other side of this narrow, tubelike portal is not Shadowfell; it is someplace much more perverse, gruesome, and chaotic than any place he has any experience with, he senses.

Charisma check: 18

Kellen cannot seal the rift the way, he learns, nor can he permanently stop its effects. But through his powerful magic and sheer force of will, he finds, with great effort, that he can suspend it for a few hours.

(Through this, Kellen understands more of the details at play here: The evil energy seeping from the rift has suffused a 300-foot-radius hemisphere with magic similar to that of a hallow spell. The effect acts as a spell cast at 9th level. While the effect is active, celestials cannot enter the area. Each time another sort of non-undead creature enters the area, it must make a DC 16 Constitution saving throw, taking 18 (4d8) cold damage on a failed save, or half as much damage on a successful one. The creature must also make a DC 16 Charisma saving throw when it enters the area, gaining vulnerability to necrotic damage on a failed save. This vulnerability ends when the creature leaves the area. ...Kellen has neutralized this for now, but it will return in 24 hours.)

Kellen

Kellen shudders as the evil energy washes over him, and eyes the spot he just closed warily. Won't last...I dunno what's causing this thing or why, but it's powerful. I was barely able to get it closed and it'll be opening back up in a day or so. Didn't seem like those...things were really behind it, so what is?

Gerrard:

Sighing in relief as the miasma that has haunted the area dissipates, Gerrard says, "Well-done, Master Kellen.  Perhaps if we collapse as much ocean bottom as possible over this whole, it might block or blunt the effect when it returns?  Can you tell if it will continue to emanate through the sea floor even if the glow is blocked?"