While undercover, an earnest detective falls in love with a criminal. But when he aides her during a bust, the pair fight to escape the country together.

After falling for a criminal, an unfulfilled undercover officer during a drug bust betrays his badge, switches sides, and fights to flee the country with her.

Just a thot...

I think the "but" needs clarification to give the twist that is implied, eg something like:
"But when he aids her during a bust and they are forced to flee the country, the limits of love and loyalty will be tested".
On her crime, the crime itself is not so much the issue as us being able to support her motivation - eg she is stealing so her dying relative can have a life saving operation or something....

I suppose what I was hoping the audience would get on board with is the idea that love and family is more important than the letter of the law? Love is the thing that makes him help her. He helps her because his feelings for her become more important than his desire to progress in his career.
Would it help if I specified the criminal is not a murderer or anything - simply a thief? Criminals are redeemed in films all the time.