He calls himself M for many reasons. Its a nice balanced letter, for one thing, strong and firmly planted, rock-steady with its tripod construction.
Ms job is to find the girl and kill her...
On a weekend visit, Brittney Ryan stumbles upon a horrifying secret at her former foster father's house. Her life is in jeopardy. She runs away to brave it alone, and turns to "lingerie modeling" in an effort to gain enough money for passage to California and an anonymous existence. Her older sister (and now legal guardian), Leitha, shows up on private investigator Nicholas Colt's doorstep, fearful Brittney will be forced back into foster care if the police are involved. A former runaway himself, Colt has a soft spot for wayward teens. He'll do anything he can to keep an otherwise good kid out of the criminal justice system.
Colt agrees to take the case.
M is not far behind.
The first two sentences are good, the last two are terrific. You've got claptrap in the middle: a mixture of cliches and howlers. Focus on M and Colt. Everyone else is just decoration.