Tarzan (book series)

===''The Dark Heart of Time'' (1999)===
{{main article|The Dark Heart of Time}}
Following ''The Lost Adventure'', the Burroughs estate authorized [[Philip Jose Farmer]] to write an official Tarzan novel, released in 1999 as ''The Dark Heart of Time''. Best known for his [[Riverworld]] series, Philip Jose Farmer has also written a number of Tarzan-based [[pastiche]] works.  He also authored ''[[Tarzan Alive: A Definitive Biography of Lord Greystoke]]'' (1972/2006), and two authorized [[Opar (fictional city)|Opar]] novels set thousands of years in the past: ''[[Hadon of Ancient Opar]]'' (1974) and ''[[Flight to Opar]]'' (1976).

Set in October 1918—during Tarzan's search for Jane—the novel takes place between ''[[Tarzan the Untamed]]'' and ''[[Tarzan the Terrible]]''.<ref name="hermes">{{cite journal |url=http://www.erbzine.com/mag9/0981.html |title=The Dark Heart of Time |first=Doc |last=Hermes |journal=ERBzine |volume=0981 |date=26 October 2002}}</ref> The novel's antagonist is James D. Stonecraft, an American oil magnate who believes that Tarzan knows the secret of immortality. Stonecraft hires hunters to track and capture Tarzan for the secret, leading to a conflicts at the "City Built by God" and the "Crystal Tree of Time". Through all of the adventure Tarzan is focused on escaping his pursuers so that he may return to his search for his wife.<ref>{{cite web |url=http://www.erblist.com/erblist/darkheartsum.html |title=The Dark Heart of Time |first=David A. |last=Adams |year=2006 |work=Edgar Rice Burroughs Summary Project}}</ref>