Aliens who attack Earth and try to control the minds of humans are common in many science fiction novels and films, both for adults and children.

H. G. Wells's The War of the Worlds (1898) also features "tripods" who attack England and who, at least to some extent, use sympathetic humans to help them. Robert Heinlein's The Puppet Masters (1951) and Jack Finney's Invasion of the Body Snatchers (revised 1978), which has been made into several films, are in some ways quite similar to all of the "Tripod" books. A short-lived television series of the 1980s, V, also features aliens who use many of the same ploys as the aliens in When the Tripods Came.

When the Tripods Came should be read in conjunction with Christopher's The White Mountains, The City of Gold & Lead, and The Pool of Fire, in which three teen-age boys join Laurie Corday's descendants to...