Isabel Oakley wants to enter her botanical paper in the Copley Award at the Royal Society of London. But when she stays with a viscount’s family in London and helps the son decode five mysterious letters, the award is the last thing on her mind…

Ashley Newcott, a betrothed spy and cipher extraordinaire, has never seen letters like them. Desperate to uncover the contents, he asks Isabel for help, plunging them both into danger that threatens to change their hearts and lives forever.