In the center of the film \"Proud Mary\" is a woman working for one of the largest and most dangerous Boston criminal gangs. She unconsciously spreads to all who cross her way. Mary has gone a long way in a criminal world and is now considered one of the best among professional assassins. The heroine never thinks about the consequences and knows that after the next task may not go home. Murders become the main meaning of her life. She has no family, no close people, only a boss giving orders. And it completely suits her.
The life of the main heroine changes at the moment when she commits another murder. Immediately after completing the task, Mary learns that the man she killed, remained a minor child. For the first time in her life she has a maternal instinct. She takes a boy and tries to save him from a criminal life. But it only worsens the situation. Mary has to liquidate one of the influential criminal leaders. And at this time, her boss learns that this is the culprit of one of his subordinates. But he does not yet know who is responsible.