After spending time fine-tuning her gravity enchantment, Envoy and the men begin to feel a bit of cabin fever, and decide to explore the cavern that was revealed beneath the simulated battleground on the lowest level of the fire-base.

Walter is fascinated by the restrained and powered-down battle robot, but Envoy notes the dangers of reactivating it. A rope is lowered to gauge the depth of the cavern, and the result is that it is nearly 300 feet deep! After discussing several options, it's decided to strap the gravity disk to the bottom of an old bathtub, and ride it down with Icarus as pilot. While Walter and Icarus leave to but the hover-tub together, Envoy encounters the spirit of Twelve.

Twelve warns her that she may be in danger by what inhabits the caverns, but isn't alive. Something related to the gravity drive crystals that 'waits for its own' to be claimed.

Icarus and Walter bring the flying bathtub and begin loading supplies, while Envoy flies down to find a safe landing spot. On the ground, she encounters the ghost of a Silent One, and discovers its remains – including a horrible chest wound that looks like the ribs were twisted and warped.

She finds a Silent Ones data pad with a recording on it. The Silent One rants about getting revenge for being captured and having his right hand taken as source material for a human-cheetah hybrid. He vows to finish escaping and then come back and destroy every trace. He is interrupted by a blue flash, which Envoy supposes is the result of whatever killed him.

The group finds a passage to follow that could be an old lava tube, and goes on for over a mile until it ends in a flat, artificial wall. Envoy and Icarus are both showing the signs of crystal-reaction though, and the wall melts away to reveal a barrier of Sifran crystal when Icarus touches it. Envoy figures out the mathematical sequence of tones to open it up after a few tries, and they find themselves in a crystal-covered cavern housing what looks like a Sifran spacecraft and a portal arch.

And then an Aelfin voice announces that Envoy is suitable to use for replacement parts…