This was a fun and informative read about things that historical fiction writers frequently get wrong. The author points out some major blunders (without naming names) made in some of the historical fiction she’s read and even admits to a few of her own. It’s basically just an overview but things like foodstuff and animals originally native to the Americas (and Europe) are covered as well as some coinage notes, historical attitudes and presentism, how British titles and names work, and things that people get wrong with the guillotine and the French Revolution. Plus the titular underpants.
Her message can be summarized as: if in doubt, look it up. And even if you think you know it, look it up (because you might be surprised). Basically, this book calls for more research, and I may even have to go look up some stuff myself.