Robert Manning Jr.

When a fertility lab technician is murdered, details regarding her secret personal life are revealed -- leading to several possible suspects; Watson is investigated by an NYPD detective.

Gideon, Hotchner and their team reopen the unsolved case of a serial killer who has attacked someone for the first time in 20 years.

As Decima uses Samaritan's feeds to hunt Reese and Shaw, Greer (recurring guest star JOHN NOLAN) exploits Finch's greatest weakness – by threatening his former fiancée and love of his life, Grace Hendricks (recurring guest star CARRIE PRESTON) – in an attempt to lure him out of hiding.

As Reese and Shaw race to catch up with Finch, he infiltrates a maximum security government facility in a desperate mission which could mean the end for not only Samaritan, but for himself and The Machine as well.

Finch's number comes up when a fatal error blows his cover identity and sets off a series of escalating encounters with Samaritan's operatives, on the 100th episode.

Reese and Finch attempts to rescue the Machine's source code before it deteriorates beyond repair. Root fights for her life against an onslaught of Samaritan's agents and Fusco is faced with hard questions following the deaths of Dominic and Elias.