Book 5 in the Grand Palace on the Thames series.
Plot: Aurelie is a gently bred young lady raised in France. She has much of what she needs, but no real family to speak of. She is somewhat flighty and sheltered, but even she realizes that the guy who wants to marry her is a controlling monster, so she takes a lovely jeweled necklace he gifted her and took off in the night to England. Once she arrives, she lands in the Grand Place on the Thames, where she hides under a pseudonym. By fluke, a former spymaster (most recently having been released from a French prison for treason), Christian Hawkes is looking to get his life back on track. He is given a simple mission – find this flighty girl, and bring her and the necklace back. Shenanigans ensue.
Julie Anne Long is highly reliable. They are what I consider at this point to be the Long archetypes. Aurelie is a firecracker with little experience but a good head on her shoulders. Hawkes is a broody but protective and innately kind man who has led a difficult life and is looking for peace. This innate goodness also means there is no time wasted on the sort of internal anguish that might define this sort of story in the hands of another author – there is nearly no overlap between Hawkes realizing who Aurelie is and that he is definitely not taking her anywhere she doesn’t want to go.