When the english writer Christopher Samuel Youd died on Feb. 3 of this year, he was better known to the public by one of his many pseudonyms, John Christopher. That was the name under which he published his classic Tripod trilogy: The White Mountains (1967), The City of Gold and Lead (1968) and The Pool of Fire (also 1968). The original three books were joined in 1988 by a prequel, When the Tripods Came, thereby adding the Tripod series to the great tradition of four-book trilogies.
The Tripod books are young-adult science-fiction novels. They're set in the year 2100, at which...