After a fresh humiliation by booing crowds at the Queen’s jubilee, here comes another blow to the Duke and Duchess of Woke. “Revenge,” the much-anticipated book by British investigative reporter Tom Bower, may not offer much new information, but it shines as a deep dive into their psyches. The folie á deux on display here is worthy of a Highsmith novel: Two very broken people stoking each other’s rage, grievances and delusions of grandeur, believing in their unstoppable rise even as they fall ever downward. What other modern-day couple would wear their expulsion from the British royal family so dementedly,...