When Karellen reveals his appearance to mankind, the initial reaction is a primal sense of horror. The Overlords have the appearance of devils, humanity’s nearly universal symbol of evil. When Jan visits the Overlords’ home planet, he sees “the ruby light […] flooding into the ship” (191). Since the Overlords can fly, their buildings take the form of high towers. When Jan looks around outside, he sees the towers and the flying Overlords bathed in the red light of their sun—a description directly reminiscent of Hell. Jan also notably manages to get to the Overlord planet in the belly of a whale, like Jonah. In the biblical story, Jonah is swallowed by a whale because he refuses to preach to the wicked at Nineveh, but he then repents and brings the word of God to the wicked. In the novel, Jan similarly brings the human perspective to the Overlords.

The symbolism of devils and Hell illustrates The Relationship Between Science and Mysticism. What humans have regarded throughout history as a supernatural evil turns out to be part of the natural universe that they did not yet understand.