The story begins with Hansen staggering out of the Indo-China jungle, falling at the narrator's feet in a state of hysteria. Hansen is traumatized and gibbering, terrified of the jungle and its monstrous obscenities. He recounts his horrifying experience after some measure of sanity returns to him, alternating between speaking and drinking whiskey to calm his nerves.

Hansen and his companion, Haldred, ventured deep into the jungle in search of orchids. They traveled further than any white man had before, facing some trouble with the natives but pressing on regardless. Eventually, their native guides abandoned them, leaving them to fend for themselves. Hansen and Haldred reached a sullen, nameless stream where they planned to build a raft to return to civilization. For this, they needed vines that were both strong and flexible.

As they searched for suitable vines, they came across a mass of black, slick, and clammy vines that writhed and twisted among the branches of a giant tree. Hansen was immediately uneasy, sensing an evil, sentient presence about the vines. He felt as though he had touched a living, malevolent entity. Despite his protests, Haldred approached the vines, intrigued by their uniqueness.

Hansen watched in horror as the vines began to vibrate and sway at Haldred's approach, like serpents. Ignoring Hansen's warnings, Haldred touched one of the vines, and it instantly wrapped around his wrist, pulling him into the writhing mass. The vines ensnared Haldred, crushing and tearing him apart until he was reduced to a formless mass of red flesh. The vines absorbed his blood and flesh, feeding off him like plants absorbing water.

As Hansen stood in shock, he felt one of the vines coil around his ankle. Panicked, he cut himself free with his knife, noticing an oily liquid dripping from the severed vine. He fled the scene, glancing back to see the vines smeared with Haldred's blood, swaying and nodding in a grotesque dance.

Hansen's tale ends with a dire warning about the serpent vines, suggesting that their roots are set in Hell and that they are a monstrous incarnation of the jungle's evil. He expresses a fear that these vines might one day burst forth upon the world of man, bringing their horror with them.