You did it! We figured this one out! It is a truth universally acknowledged (by me for certain) that the Bitchery pretty much knows everything, and really, it's true. Scroll down to see the solution for this HaBO - and many thanks!
This HaBO request is from Susan, who is searching for a historical romance:
Hero’s backstory: He is the son of a Duke (?) and his mom hates his dad so much she drops the hero off on the London docks/Thames waterfront when he is a small child. He gets put to work as a mudlark along with other young boys. When he is years older, maybe 8 to 12 yeas old, his father somehow finds him and takes him back into the life he should have led.
He’s married and the heroine also has a troubled past. Her mother died in a carriage accident on a bridge over the Thames, and there is some controversy about a missing necklace. In the end the hero proves his love by using the mad skills he developed as a child (as if, just got to love these bananas books!) swimming underwater. He dives down and miraculously finds the lost necklace.
How deep is that dive?