That means your murder mystery has to start with an interesting sleuth.
Being smart, attractive, and witty with the puns doesn’t cut it. In a murder mystery (and really any modern novel) an interesting protagonist has a character trait that readers identify with. They feel a connection to the character, and can empathize with what makes that character tick. When you think about it, characters that have a strong desire to achieve something – whether that’s overcoming an internal struggle or finding love, freedom, forgiveness, acceptance – have the strongest impact on readers.
There’s an inherent tension in wanting the Protagonist to achieve his desire, but also knowing that he may fail. It makes great character drama.
So how do you write this?
Well, first establish the Protagonist’s desire. This is different from solving the murder mystery. This is an individual and deeply personal need of your main character. It could be to reconcile with a family member, to seek forgiveness for a past accident, to return home, to overcome an addiction, etc. What would be unique to your main character’s life or personality?
Second, define what obstacles are keeping your main character from achieving this desire. If it’s to reconcile with a family member, what’s keeping them apart? What’s preventing him from receiving or accepting forgiveness? Why can’t he go home? Is there an enabler in his life that’s preventing him from overcoming the addiction?
Finally, establish the stakes. What terrible consequences will result if he doesn’t achieve his desire? Will he never find love? Lose his family? Never see his son again?
This internal drive serves to make the Protagonist relatable to readers. This desire should affect the main plot as well, providing a stumbling block or two while solving the murder. And, if you can come full circle, tie both plots together in the end so that the Protagonist achieving his desire allows him to ultimately identify and catch the murderer.