Question: I am writing a murder mystery and the story goal at first would seem to be that the protagonist(female who discovers dead body) solve the murder. However the story really is going to develop into her falling in love with a good man (police officer) and avoiding the premise in secondary plot of protagonist's ex coming to kill her.
So should my story goal be searching for true love?Answer:
In dramatica theory, there are four throughlines to any complete story.
1. The overall throughline (external problem).
2. The main character throughline (internal conflict).
3. The impact character throughline (the alternative approach).
4. The relationship throughline (the progress of the relationship between the main and impact characters.
The impact character can be the villain, but in romantic stories it is usually the love interest. In this case, you also have a third candidate for impact character (the murderous ex). You should choose one of these possibilities, but either way, the impact character is the person who forces the main character to question her approach by offering an alternative approach.
Typically in romances, the relationship throughline is given more emphasis. The overall throughline may be just a vehicle to force the couple to spend time together so that the relationship can bloom.
On the other hand, many mysteries feature the relationship throughline as more of a subplot or perhaps balanced with the overall throughline (as in Agatha Christie's Partners in Crime
The story goal is part of the overall plot and is the concern that involves or affects the majority of characters. For example, I'm guessing most of the people your story world have an interest in seeing the murderer brought to justice (or perhaps the opposite in some cases, if the killer has allies). However, the other three throughlines will also have their own focal point of concern.
In a murder mystery the story goal is usually finding out "who done it" and how, or in some cases capturing the murderer.
The relationship plot is usually about how the relationship evolves and the concern usually involves the couple conceiving a new idea about each other or perhaps changing as people. (That's your romance.)