This topic came up before, but in my first attempt to write a mystery, the first 100 pages focus on developing the romance, although there are clues along the way to what in retropspect is part of the solution. But the reader does not know that.
Then the latter 160 pages is the obvious murder (previously a murder was certified as an overdose, but not know until later), and the solving of it by the team of lovers.
I thought it was a failure because it was not a true mystery. Is it pretty much doomed because the murder and investigation doesn't truly begin until 100 pages into it? What is ideal?