The novel contains many themes which are common in Wyndham's work: a depiction of the Soviet Union as an opaque, inscrutable menace is presented in Chapter 2, a central problem made worse by human greed and bickering, and a firm determination on the part of the author to not explicitly detail the origin of the threat faced by the protagonists. Other themes include the dissection of human nature from a range of standpoints, and male and female gender roles.
Wyndham's narrative also focuses on the pragmatic issues of self-sufficiency facing survivors of such a catastrophe. Simply living off of scavenged canned food from London shops is not a viable survival strategy on a scale of years. The enclaves that survivors set up in the countryside to attempt to rebuild civilisation cannot simply use scavenged ploughs forever, but eventually need to develop the capacity to build their own.