This is a reasonably written character assassination. Kelsey's case theory is simple - Drake was a thief with a ruthless streak, who bungled his way to riches and a 'round the world trip, and who manipulated the religious and political differences of the time for his own ends. Kelsey never wavers from this. His objective is to kill the hero. Which is where Kelsey loses his balance and lets the book down.
Obviously well researched, the narrative is coloured throughout by prejudice. And whilst fairly easy to read, the need to denounce Drake becomes stylistically palpable. For instance Kelsey has the habit of repetition, even within the same paragraph; and the rhetorical closing section is clumsy - like an A Level student trying to wrap up an exam question in the last five minutes. All this is based on the fact that throughout a five hundred-page book Kelsey has no sympathy with his subject. He is a barrister for the prosecution and getting a conviction is all that matters.
Drake himself remains an enigma, perhaps even more so after Kelsey's attack. Not once does he make a proper appearance in the narrative. Hostile witnesses give their evidence, Kelsey puts his own biased interpretation of events, and all the while El Drago looks placidly back from his portrait. The Shillingley narrative isn't referred to at all.
While there's certainly evidence that Drake's story is not simply 'Kelly's Heroes' in a galleon, this biography is too biased and with too little understanding of the man to make a proper, rounded study.