Paul Christopher, septuagenarian and former superspy, was last seen in a remote Chinese province. His ashes are delivered to his cousin Horace, also a retired spy, who is not convinced that the ashes belong to Paul. Then he learns that Paul is on the trail of Ibn Awad, a mad sultan with nukes who covets a first-century manuscript (a Roman spymaster’s report on Jesus) that is thought to be in the possession of Paul’s 94-year-old mother, who hasn’t seen since 1940, when she was abducted by the Nazi Reinhard Heydrich. So Horace recruits a handful of creaky-kneed retired spies and goes after Paul.
If you can get over the wild improbability of the plot, it’s actually well-written, coherent, and plausible on its own terms.