As a plot , they could look for Sonja's body (without finding her) and for her near killer. It would make sense. At last, until they all end up on the kidnapping case.

I would reserve "the first assignment" for the next story, I think it deserves it, and also it should feature a previous meeting of all the members (even past ones . hint hint ) and a careful planning before entering in action... now that I think of it, "The First True Assignment" could ba good titale for the next story...