I think he was writing mostly in the 1920s and 1930s. The introduction to this novel spoke about how most of his novels weren't published until after he was dead. Instead they were published as serials in the newspaper, written week to week with very quick deadlines.
The language is true to the times, particularly the way that the characters spoke. From his writing, it's also apparent that he had a strong connection to rural areas and people, and seems not to be naive about the realities of particular industries (such as the horse racing industry in this case).
His novels are many mysteries, and he went on to write lots (29) of novels with a main character who was an Aboriginal half-caste, detective Bony. From having read this novel (and another one which I will write up in a couple of weeks), so far his mysteries are excellent. They are not like modern mysteries where the investigators rely heavily on forensic science and technology. The detectives in Upfield's novels use their brains, and speak to people. The other fresh thing about his writing is that there are no clues to the reader about who has done it - it truly is a mystery all the way until the detective reveals the solution to the readers and the criminals together.
Simply written, but really endearing, and truly captures the feeling of the time.