Deception and lies
Gareth’s father lied to him his entire life about his true parentage, having been born from an affair his mother had with another man. As such, his father kicks him out of their family when is a young man, making Gareth resent him for the remainder of his life. However, Gareth is more similar to his father than he realizes, as he also dupes Hyacinth into his web of lies and fails to tell her the true reasons behind his desperation to find the missing jewels.
Unexpected love
The relationship between Hyacinth and Gareth is both unexpected and unwanted. Having refused an arranged marriage years ago, Gareth is not interested in marriage. Similarly, Hyacinth has turned down numerous proposals and seeks to live her life as a spinster. The two do not intend to fall in love yet fate seems to intervene in a way no one can intend.
Social status
Though Gareth spends most of the book attempting to spite his father by inheriting his title and locating the family jewels, he also fears that his true illegitimate parentage will be revealed. This leads him to make poor choices and lie to Hyacinth about the true reasons for wanting to find the jewels. It is clear that Gareth fears social ostracism and wants to avoid it at all costs.