Richard Marsh 
Datchet Diamonds 

The story begins with Miss Daisy Strong who has met a rather fascinating young man named Mr Lawrence whilst in Brighton. "He was holding her hand in his, and looking at her with something in his eyes which there and then she told herself would never do." Unfortunately, she is already engaged to Mr. Cyril Paxton, a feckless speculator on the stock market. Mr Paxton is always claiming to be on the next big thing and has consequently lost his fortune. Daisy gives him an ultimatum – make your fortune back or we can’t be married – and, of course, Mr Paxton goes and loses it all in a final disastrous speculation. (Goodreads)