Two on A Tower may be considered one of Hardy's minor novels but it's a wonderful little novel in its own right about Lady Viviette Constantine, who has been abandoned by her husband and her love for poor astronomer Swithin St. Cleeve, who is almost ten years younger than her.
Admittedly, it does not maintain the lyrical fascinating beginning where Viviette first discovers Swithin's astronomy and they conduct his studies together. I have no interest in astronomy and yet when Swithin obtains a grand piece of equipment, it is exciting. His love for astronomy is the highlight of the book, as well as his tragic flaw, and Swithin is one of my favourite Hardy males. In some ways he's a bit like Jude but more intelligent and sympathetic.
A lot of melodramatic contrivances follow but the novel is still a pageturner. Anyway, Shakespeare used more contrivances than anyone, and Hardy openly states that the novel is a 'romance', not to be viewed realistically.
If you take the novel seriously, however, there are a lot of interesting themes to be discovered. The discussions of science were incredibly topical for nineteenth-century readers and still are now. Through Viviette, Hardy reveals the plight of respectable women forced to remain constant and isolated when men can simply get up and go. It's a beautiful depiction of a sad truth of the times. The forbidden relationship is dealt with nicely: one can sense Viviette's awkwardness when people refer to Swithin as a boy or 'youth'.
This may be minor Hardy but it's still fascinating. It is also completely charming- later in his career, Hardy lost some of this charm, hence why he is thought of as depressing and bleak.