If your MC is some kind of detective or police officer or whatever, somebody that addresses crime, and Matt is seeking help from them, then you probably have to have Matt explain and prove he is a good guy.
The MC is unlikely to just believe whatever Matt says; a detective doesn't live long if they can be so easily convinced of a lie.
So your MC is going to be suspicious, and ask questions. Also, detectives are tough in the sense of not being distracted by emotional clients, whether they are in grief or angry or anything else. Matt cannot just insist on help without proving, to some extent, he is sincere and deserves the help of the MC.
So whatever backstory there is, it is the MC's job to extract it, and decide whether the girlfriend really is in danger and whether he believes enough of Matt's story to take some first actions, investigate, and see where to go from there.
As an author, you need to put yourself in the mindset of the MC, who doesn't want to be tricked, and is somewhat cynical about everybody's ability to be honest with themselves. Then some guy shows up and tries to convince him this girl Ella got kidnapped for no reason at all, a big misunderstanding ...
Riiiiighhht. That's gonna take a lot of explaining, about what the kidnappers think happened, and why they think it deserves revenge, and why they didn't just kill Ella (if it is just revenge why hold her, why not cut her head off and leave it on his doorstep?), and what Matt has done to correct it (or exacerbate it).
And in the end the MC may not believe Matt's claim of innocence, but might believe Ella is innocent and kidnapped, and proceed on the basis of saving a damsel in distress.