Written in the 19th century, this lengthy and thorough text documents the various manifestations of demons and devils in the Christian religion. The forms they take, and the means by which they appear in the physical world, are cataloged. How they correspond to actual phenomena, such as death and pestilence, is likewise noted. Conway draws upon various writings within the Biblical scriptures, together with later works published in the Middle Ages and subsequent centuries, to arrive at his own comprehensive treatment of the subject.

The second half of the work concerns devils. Various figures such as Ahriman and Viswámitra receive chapters, in which the writings about them are quoted to form a complete image of their behavior and meanings. Appearances of devils in later works, such as the diabolical Mephistopheles in Goethe's Faust, are also cataloged. The overarching aim of Conway's thesis is to draw parallels between the various demonic and devilish phenomena, while noting their overall influence across the history of Christianity.

The text is informative in tone and does not stray to dogmatism; Conway instead provides sourced information in a factual, studied tone. For his part, Conway was not a believer in the lore of demons. Although he served variously as a Methodist, Unitarian and Freethought minister in life, he had little time for the supernatural elements of Christianity. It is thus that Demonology and Devil-lore is an effort toward debunking and discounting what Conway viewed as the fantastical elements of a faith he otherwise identified with spiritually and morally.

Today, Demonology and Devil-lore is somewhat archaic in terms of tone owing to its age. However, it still counts among the most thorough, in-depth and wide-ranging treatments of a subject which has fascinated religious and non-religious persons alike for centuries.