Sinkholes are a terrifying force of nature as miles of ground can disappear into nothingness with no warning, taking everything on the surface with them. When they happen in a populated area, the news and media love to show images of death and property destruction. People don’t realize that this phenomenon occurs underwater, as well.

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When a giant sinkhole opens in the Antarctic Ocean, just off the Ross Ice Shelf, a huge research facility is transported there to run tests and map the fissure. After one of their first exploratory drone submersibles is hopelessly mangled by an unseen force, the researchers send a manned sub down for a rescue operation. The crew is troubled by oddities such as caverns cut into the sides of the sinkhole walls, an unexplained temperature change in the frigid Antarctic water, and an aggressive sea monster of unexpected size.

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The sea monster shreds the sub and disappears back into the depths.

The leadership aboard the research station decides to send down another sub, this one equipped with offensive weapons, to figure out what’s going on and eradicate the threat hovering directly beneath them. When they reach the original kill depth in the sinkhole, though, the outcome is anything but certain.