Literary sins

I just finished a book that's a historical mystery, a genre that's becoming increasingly popular, with historical figures either participating in solving crimes or being part of the cast. Jane Austen and Charles Dickens are two who have been so featured.
The book I just finished was about Charles Darwin, one of my heroes. In the book, an intelligent, brave, strong, handsome man and his intelligent, brave, strong, beautiful partner unearth a succession of manuscripts that prove that Charles Darwin stole the theory of natural selection (The keystone of his whole theory) from another man and may have actually killed the other guy, the HMS Beagle's naturalist, Robert McCormick.
The novel infuriated me. I almost couldn't finish it, for two reasons. The first is that the novel is dishonest in its craftsmanship. What the author proposes is wildly improbable, so he constructs a giant, intricate god in the machine to make it all happen. The protagonists discover not one, but four manuscripts which do not so much fill in gaps as create the story of Darwin the plagiarist. Without those "discoveries" there would be no story. It's not as if the author were tinkering with history -- he's inventing it. It is part of the writer's craft to make what happens seem natural. The possibility that there would exist four manuscripts, each linked to the other, and each meshing with the others into a seamless narrative, well -- that's a little too much.
Also, so much of the novel revolves around the Beagle's surgeon, Robert McCormick, who, according to the published record, left the Beagle in 1832. In the novel, he came back on board, and died in a volcano around 1834. In reality, McCormick outlived Darwin, traveling and writing copiously until he was retired in 1865, and dying in 1890. So, the novel contradicts the available records, which is, at least, clumsy.
The second reason the novel infuriated me is that the author has basically slandered the name of one of history's greatest scientists. If there were suspicions abroad, I might (just might) understand the motives, but there's nothing around to suggest that the author's thesis is even remotely near correct. It's made up of whole cloth for one reason, to sell books.