R. Kent Tiernan joins Andrew (Twitter; LinkedIn) to discuss the seven-year covert operation to execute Mary Queen of Scots. Kent is the author of The Walsingham Gambit. 

Elizabeth I, daughter of Henry VIII and his second wife Anne Boleyn, survived no less than 9 elaborate plots against her life. In an era of religious conflict and constant power struggles, it was perhaps more important than ever to run an effective intelligence service. 

R. Kent Tiernan previously served as an intelligence officer in the United States Air Force, and an assistant professor of history at the United States Air Force Academy. Kent also served as the Vice Chairman and Staff Director of the Foreign Denial and Deception Committee before retiring in 2014 at the rank of Senior National Intelligence Service officer.

Our analysts do a wonderful job, but it's very difficult for them because they're looking for continuity or congruity in the information, uh, in order to come up with an answer or a best evaluation of truth. Our job was looking for incongruities in the information. Uh, things that didn't make sense the other evidence was leaning one way, but then we'd get a bit of evidence, and it just didn't make sense to what we were seeing, uh, normally.

• Elizabeth I famously had a sweet tooth – A habit that would eventually cause her teeth to go black in an era of subpar dentistry. One of her favorite sugary treats was candied violets – A less popular snack nowadays, but just as tasty!