Towards the end of the third season, Agent Donnegan (Lauren Lapkus) started getting closer to the truth of who was behind the money laundering.
As viewers will recall, it was a visit to the nail salon which helped her work how they were counterfeiting money.
This led her to make the link with Ruby and headed to get her nails done by her.
After Ruby checked the note which Donnegan gave her, this convinced the agent she was behind the crime.
She swiped her phone, which gave her the evidence she needed of who Ruby was working with.
The last viewers saw of the series was her heading towards Ruby, Beth and Annie in the park.
Good Girls season 4 begins on March 7.