WARNING: The following contains spoilers for Netflix’s Lost in Space, streaming now.
The third season of Lost in Space finds the 24th Colonists Group separated. The adults are in the "Danger" system, skulking in the shadow of a star to avoid detection by the avenging mechanical hordes and all 97 of their children are grounded on a mostly destroyed planet hoping not to be pummeled by rogue asteroids.
Led by Judy Robinson, the children have developed an efficient system for survival and Will Robinson has been charged with repairing their thruster by scavenging titanium ore from the planet. They eventually cull enough raw material and set about the repairs so they can try to launch before the ever colliding asteroid belt ringing the planet makes escape impossible for the Jupiter's autopilot to navigate. Will takes the opportunity to spend their last 19 hours planetside to explore some newly found alien ruins, and suffice to say, no one will ever have the chance to continue his "work."
On the same day that Judy's crew prepares to depart the world they have been making habitable for the last year, Robot mysteriously disappears. A search takes place and Penny, Dr. Smith and Will eventually locate a slightly hidden cave entrance to an alien labyrinth with still no sign of Robot. They venture inside and find a few things of note. First are obvious signs that the area has been tunneled and therefore is not a naturally occurring cavity, a point that is brought into stark relief when they come to the end of the winding path and come upon a mechanical door. The second is a set of prints that seem identical to Robot's, except Will notices a few distinguishing features that lead him to believe that what he is investigating was made by something organic.
Shortly after making this discovery, they come across Robot who leads them further into the interior of the underground structure and informs them, or more accurately, Will intuits that this is the place where Robot was built. Robot shows Will a little bit more, which is enough to whet his scientific curiosity and for him to return later. When Will comes back on the day they are set to launch, he brings a camera with him so that he can document what he finds in the ruins.
One of the first things he comes across is the skeletal remains of one of the original inhabitants of the planet. After a cursory examination of its structure, it is clear that the AR's (Alien Robots) hostile four-armed configuration was based on the phenotype of their creators and not for some other utilitarian purpose. This revelation not only sheds light on the common psyche between humanity and these aliens, with each building automatons in their own image, but also suggests that the humanoid form that Robot adopts after befriending Will is not some default posture, but perhaps an attempt to assimilate and ingratiate with its new companion.
Will delves further into the catacombs and comes across a dark pit. After trying to pierce its gloom with the naked eye, he pulls out a flare gun and fires it into the abyss, scattering shadows and illuminating a macabre tableau. Beneath him are curving archways, like underground boulevards crisscrossing and layered, descending into the depths and each of them is littered with bones, intact skeletons of the planet's dead natives. The flare itself seems to have been ill-advised if Will's goal is to keep the ruins as pristine as possible for study and preservation. He wasn't aware of any petrochemicals, alien vapors or gases that could potentially ignite but he already knew that much of the damage he had seen was the result of volcanic activity. A flare may not have credibly awakened any dormant igneous reactions but it smacked of short-sighted recklessness.
He eventually comes across an alien control panel that appears to require an alien handprint to activate, so he returns to the original outer chamber and snatches a forearm off of the first skeleton he finds. He takes the bony appendage, which may have some formally fleshy residue still clinging to it, and proceeds to interact with the panel. Immediately, a tone bellows out that sends gentle tremors throughout the cavern and the tone itself is reminiscent of sounds he has heard before emitting across their instruments when intercepting AR transmissions or technology. Will hypothesizes that instead of interference, these sounds may have always been some type of communication, and further posits that perhaps one of these sounds might be effective in stopping the AR in their tracks.
The logic train departing that station of conjecture is never really fueled by anything resembling reason, a trait shared by many of Lost in Space's intuitive leaps, but it does prove to be accurate when put into practice. However, in the moment of eureka, Will is so convinced that he sets out to recreate every tone possible, even as each one creates larger seismic activity and generates heavy plumes of loose rock that drift from the upper reaches of the cavern. As the entire structure begins to collapse in on itself, Will continues to bone-arm his way into more alien recordings like a doomsday DJ until he requires rescue in the form of Judy and Dr. Smith.
The cavern, its purpose and its secrets are all presumably lost. There was an above-ground settlement that the Robinsons never saw but Robot views from a distance at the end of Episode 2, so some research material may still exist. It could also be just as likely that the structure that seemingly crumbled under the weight of the panel's sonic droning was situated underneath that same settlement and could have done irreparable damage to both sites above and below. Lost in Space ends with Will and Robot jaunting around the galaxy willy nilly, boldly exploring new worlds and potential new civilizations, but it is hard to imagine Will could have graduated from Starfleet or impressed Lara Croft with this archaeological disaster on his resumé. The AR creator civilization is the only proof of non-human intelligent life in existence and Will buried what may have been their last refuge before their cataclysmic fall to pirate some alien audio files, their eventual use to him notwithstanding.
Lost in Space Season 3 is currently streaming on Netflix.