The series follows the tragedy that occurred when terrorists attacked at the annual Boston Marathon on April 15, 2013. They carried out the attack by placing two homemade pressure cooker bombs which detonated near the finish line of the race 14 seconds and 210 yards (190 m) apart. That resulted in three fatalities and hundreds injured, including 17 who lost limbs. With the help of archive footage, interviews with investigators, witnesses, survivors, and occasional reenactments, it offers details about the FBI investigation into what was quickly deemed a domestic terrorist attack. In the first episode, hours after the blasts, investigators pore over evidence. One photo and a few seconds of footage lead to a breakthrough - and an agonizing choice.
Former students of Archbishop Keough High School reveal allegations of sexual abuse by Father Joseph Maskell, the chaplain of the school. It details the personal story of 'Jane Doe' (Jean Hargadon Wehner) who claims that Father Maskell took her to see the dead body of Sister Catherine Cesnik in Lansdowne, Maryland.
Jean Hargadon Wehner discusses how she came to remember years later the sexual abuse she suffered at Archbishop Keough High School. She also talks about what happened when she reported the abuse to Church officials and how she realized she was connected to the death of Sister Cathy Cesnik. As the can of worms is opened on the hidden world in the high school and the people begin to talk about what happened behind closed doors. With the Jean’s accusations, Abbie Schaub, Gemma Hoskins, and Tom Nugent learn about a story of a graveyard and a source nicknamed 'Deep Throat' who could hold the key.
As Michelle's loved ones cope with her sudden death, her work to unmask the Golden State Killer lives on. After inheriting Michelle's 37 boxes of case files, Paul Haynes and Billy Jensen work alongside Patton Oswalt, to finish her book.
Deep Throat comes forward with the orders of anonymity with the horror story of what happened in 1994 with the charges against Maskell. With the location of a secret grave of documents, Deep Throat’s story contradicts the story of the former state’s attorney Sharon A.H. May. The group begins to investigate Dr. Richter who worked with Maskell to groom girls and their families. As the case prepares for a potential trial, the disappearance of Father Maskell causes problems as the prosecutors find themselves defending the idea of repressed memories. When things fall apart, victims still find themselves seeking justice. Abbie and Gemma seek the links between Jean and the killer... which leads to a man named Brother Bob.
In the first episode, hours after the blasts, investigators pore over evidence. One photo and a few seconds of footage lead to a breakthrough - and an agonizing choice.