The following morning the heroes awoke to find Captain Marshall missing, supposedly abducted; his tent is torn on one side and a trail leads into the jungle. Despite objections from the crew, MacIntyre leads the heroes with a few “volunteers” to rescue the captain. Convinced that the answers to the island’s mysteries lie behind the stone door, they set out towards the hollow.
Following Javier’s charts to the door, the heroes place the keystone in the slot his notes indicate, but as the door begins to lurch open, it suddenly jams and cracks almost in two. A sharp hissing noise from behind it ends in a sudden eruption of flame, as the door is blown to dust in an explosion, killing one of the sailors and surprising the heroes; the reek of gunpowder raises questions as to the source of the danger on the island.
Descending into the depths of the island beneath the hill, the heroes find a tunnel where, at one point, the walls are coated by a stream of acidic fluid, though it seems to serve no purpose, being harmless unless disturbed. At the end of the tunnel the path opens into a great cavern, the walls of which glisten like silver or the night sky; at the centre of the cavern, stretching from the roof to unfathomable depths below, stands a giant tower, clearly not of human origin, its sides smooth and dark as obsidian.
Exploring the tower, the heroes find little of interest until they reach further down. In a room off the central staircase they find the grisly remains of Bill, the sailor abducted on the first night on the island, and next door they discover the still breathing, but badly beaten, captain Marshall. Bill holds a small stone, similar to the keystones, but dark blue in colour, which the heroes prise from his grasp. When they use gunpowder to blow open the iron bindings holding Nathan in place, though, an inhuman roar bellows from the deepest depths of the tower.
Whilst MacIntyre beats a hasty retreat with Marshall’s unconcious form, Leni and Rosa stay behind to hold off whatever terrifying beast emerges to confront them, but fear gets the better of Carlo, who decides that discretion is the better part of valour for the time being. When the beast lumbers its way up the stairs, the two heroes awaiting it are shocked by what they discover.
The beast is a massive, inky black monstrosity of claws, teeth and chitin. Its very outline shimmers and blends with the shadows their torches throw off, and its burning red eyes threaten to pierce their courage. Weilding its blade-like claws and some mysterious alien gun-like weapon, it overwhelms the outmatched Leni, but Rosa’s fire magic surprises it and momentarily drives it to retreat… into the walls themselves. Frightened and shocked by this, Rosa grabs Leni’s bleeding form and retreats back up the stairs before the beast returns, and they catch the rest of the party, waiting for them at the entrance to the tower.
Together they make a run for the door at the start of the tunnel, but when MacIntyre passes by the streams of acid once again they erupt from the wall in a spray of corrosive vapour, narrowly missing the Avalonians, MacIntyre’s shield man instincts and training saving them at the last moment. Hesitant to pass through this new obstacle, the beast cathes up to the heroes, and a deadly fight ensues between the beast and those who hadn’t yet made it to the other side of the acid streams. Taking an opportunity to escape, Rosa dives to the other side of the streams, barely avoiding another spray of acid, and the beast, which has focussed its attacks towards the young Castillian since her fire magic first scared it off, vanishes once again into the shadows on the walls.
As the party flees, they see the beast reappear on the other side of the streams, seeming to flow out of the wall. It gives chase, but they escape to the door before it catches them again. Wounded, tired and with two of their number unable to fight, the heroes seem to be on the verge of defeat, before Rosa reaches deep into her power and devastates the beast with yet another massive gout of sorcerous flame; its outline seems to burn away in the heat, melting down into the shape of a human, now badly scorched by the sorcerer. The man, dressed as a knight in armour, coughing and in pain, yells something indecipherable in Eisen before vanishing yet again into the shadows, reappearing further down the tunnel.
Carlo, eager to make up for his earlier misjudgement of his foe, gives chase, all the way to the very base of the tower. When he gets there, however, he finds the man standing over a massive store of gunpowder, rigged to blow the entire tower to rubble. The man offers him one chance to escape, which Carlo grudgingly accepts, beating a hasty retreat back up the stairs. Halfway there, a massive explosion rocks the tower, which starts to collapse into the pit below it, filled with acid from the streams which the tower itself seems to pump in its central column; Carlo narrowly avoids being struck by jets of the liquid as the column cracks and breaks, and dives to the safety of the tunnel just as the tower falls toward oblivion below.
The explosion and the collapse cause the tunnel to start caving in, and the heroes narrowly escape being trapped, Carlo making it out just as the entrace falls into a cloud of noxious dust behind them.
Returning to the camp, they find the ship just ready to leave, and sail away from the island for good.
The New Horizon drops the heroes back at Little Carleon, where a recovered Nathan apologises to them for the danger they faced on his behalf, and his misjudgement of his crew’s readiness to tackle such ventures. They turn the stone into the Explorer’s chapterhouse, Luthon paying a minor comission for what he describes as a pitiful find; a single “stormstone” of which the Society already has several well catalogued examples.
Though he appreciates their help, Nathan parts ways with the heroes, telling them they are better seeking their fortunes without his bumbling efforts getting in their way for now, and books them passage on a Voddace merchantman, Veritus, that is docked beside the New Horizon, due to sail the following morning…