Blue Bloods Season 13 Episode 20 revolves around challenging relationships, especially mixed with police work.

When someone sends flowers to Danny's precinct with a condolence card, Baez realizes that it's a threat against her. Sam Evans, a psychopathic killer she put away years ago, just got out of jail.

Danny and Baez talk to Sam, who says he's a changed man and had lots of time to think in prison. Soon after, Baez's nanny calls. She found an open door when she returned from a walk with Elana. Danny investigates and finds a flower in Elana's crib.

Baez stays with the baby while Danny checks out a lead. But when he finds out where Sam is, Baez goes to the scene, determined to end this for once and for all.

Meanwhile, Anthony's goofy cousin Joey asks to stay with him. Joey loses his key and someone shoots at him and Anthony while Anthony is getting him a spare. Joey admits that he owes money to a mob boss that Erin has been trying to get enough evidence to prosecute. Anthony wants to use Joey as bait but Erin thinks it's a bad idea.

Finally, Frank learns sad news about a friend and Eddie tries to help Badillo's ex after she is assaulted.

To find out what happens, watch Blue Bloods Season 13 Episode 20 online.