Ransom My Heart by Meg Cabot
When beautiful, spirited Finnula Crais kidnaps the dashing knight Hugh Fitzstephen, she has no idea that she's ensnared the new Earl of Stephensgate on his way home from the Crusades. Nor does she realise that Hugh is quite happy to be kidnapped by an enchanting tomboy, and will do anything it takes to avoid being rescued. With Finnula determined to hold Hugh to ransom, and Hugh equally determined to steal Finnula's heart, it isn't long before the fireworks start! And just when it looks as if there might be a happy ending, disaster strikes. When an attempt is made on the new Earl's life, there is only one suspect - and even if he loves her dearly, Hugh can't let her get away with it . . .
Ransom My Heart is a risque historical romance written by Princess Mia Thermopolis of Genovia (with a little help from Meg Cabot), as featured in The Princess Diaries series.