The Plot:

Kim Jongin (Kai) is a former dancer and choreographer, and worked at a dance studio together with his best friend, Lee Taemin. 

One day Taemin was found murdered in his apartment.

He wants to know who killed Taemin and wants revenge.

Do Kyungsoo (D.O.) was unemployed and had a girlfriend.

One day on a date with his girlfriend, she got shot in front of him and died after that.

He didn't see the person, who shot her, but he wants to find out.

One year later Jongin and Kyungsoo are now working together as detectives.

While working they also start falling for each others.

Your choice on the story:

Who is the murder?

1. Someone from EXO

2. Jongin killed Kyungsoo's girlfriend and Kyungsoo killed Taemin. (That would be kind of a cool twist, but that would make no sense at all)

3. Someone, who hated both Kyungsoo and Jongin.

4. other

When did they first meet each others?

1. At kindergarten (childhood friends)

2. When both of them got the job as detectives.

3. other

Some scenes that I think would be a good idea to have in the story, but you don't have to write this in your story: 

@ Rest of the EXO members appearing

@ Hardcore se... I mean.... kiss scene. 

@ A lot of action

Ideas for titles:

Love and Crime

Love and Revenge

Revenge Detectives

Kill My Friends And I'll Kill You

(You can find better titles)

I dunno how much of a mystery fan you are, but I hope you like your plot.