The Garden Intrigue (Pink Carnation #9) by Lauren Willig

In the ninth installment of Lauren Willig's bestselling Pink Carnation series, an atrocious poet teams up with an American widow to prevent Napoleon's invasion of England. Secret agent Augustus Whittlesby has spent a decade undercover in France, posing as an insufferably bad poet. The French surveillance officers can't bear to read his work closely enough to recognize the information drowned in a sea of verbiage.