Paula Cassidy was an NCIS Special Agent who mainly worked from the Pentagon and also spent some time in Guantanamo Bay as an interrogator.
She was later transferred back to Washington D.C. before being reassigned to the Pentagon, becoming the leader of her own team which she led up until her death in the Season 4 episode, Grace Period (episode).
NCIS Season 1
Cassidy made her debut appearance in Minimum Security (episode) where at the time of her debut, she was working as an interrogator in Gitmo or Guantanamo Bay.
When NCIS Agents Leroy Jethro Gibbs, Anthony DiNozzo and Caitlin Todd arrived to investigate the death of Khalil Sa'id, a Petty Officer who had worked at Gitmo prior to his death, Cassidy was left out of the loop because of five un-mailed letters of hers had been found in Sa'id's personal belongings and as such, Cassidy was a suspect.
She was later cleared although she developed a strong resentment of Gibbs and the others for keeping her out of the investigation.
During that time, she and DiNozzo flirted with the possibility of a romantic relationship. Paula was later shocked to discover that Sa'id had been in league with Nassir Al-Jazair and the two had been planning to kill Tariq Abassi, one of Bin Laden's son-in-laws, but Cassidy intervened to stop the assassination, shooting Nassir in the shoulder as she didn't want him to become a martyr.
Cassidy's final appearance of Season 1 came in the Season 1 finale episode, Reveille (episode).
NCIS Season 2
Cassidy returned in the Season 2 episode, Heart Break (episode) where it was revealed that she had become an Agent Afloat on the USS Kennedy.
She helped the team with a case regarding Michael Dornan, a Navy Commander who had died after having a successful surgery being performed on him.
She later returned to NCIS HQ where she revealed that Dornan had asked her not to file a report on a young Ensign and as such, Gibbs berated her for not revealing a possible suspect and for looking the other way.
NCIS Season 3
During the interim between Caitlin Todd's death in Twilight (episode) and Ziva David being assigned to Gibbs's team in Silver War (episode), Cassidy was temporarily assigned to the team, serving as DiNozzo's partner in the episode Mind Games (episode).
NCIS Season 4
Cassidy's final appearance was in the Season 4 episode, Grace Period (episode) where she lost two of her team members, Agents James Nelson and Rick Hall to a suicide bomber. The aftermath left her emotionally scarred and distraught as she began blaming herself for what had happened, resulting in her developing and experiencing survivor's guilt.
During the investigation, she resented Ziva's attitude and the two were shown to have a hostile relationship with Paula often getting Ziva's surname wrong on purpose.
At the scene, Cassidy discovered that Jamal Malik, the true mastermind was attempting to kill everyone. She then jumped on him with the doors closing behind them despite Gibbs and Tony trying to come to her aid as she and Malik struggled for control of the device.
However, Malik set the device in motion and in her final moment, Cassidy saw a vision of both Hall and Nelson standing alongside her.
Seconds later, the bomb exploded, shaking the foundations of the building while also killing both Cassidy and Malik. Cassidy's death left the team, especially Tony devastated with his talk with Cassidy later giving him the courage he needed to tell his girlfriend that he loved her.
NCIS Season 6
In the last few seconds of the Season 6 episode, Collateral Damage (episode) where it was revealed that at a bar there was a wall dedicated to those who had died in the line of duty with Cassidy's photo being among them.
She was mentioned in the Season 6 episode, Hide and Seek (episode) when the NCIS team reviewed an old case of hers.
Despite being an NCIS Special Agent for six years, Cassidy often made rookie mistakes. This was first revealed in the Season 1 episode, "Minimum Security" where she had suspicions in regards to both Sa'id and Al-Jazair but had let them slide yet she later came to regret it.
When Cassidy returned a year or so later in the Season 2 episode, "Heart Break", she ran into trouble yet again when she stated that she hadn't filed a report on a possible suspect, Ensign Evan Hayes because the Commander, Michael Dornan, had asked her not to.
Gibbs was furious at her for doing this and said that NCIS Agents weren't supposed to look the other way. This in turn resulted in Kate being forced to shoot Ensign Hayes when she thought he was about to fire at Gibbs.
She also seemed to get very emotional as seen in "Grace Period" where after losing her team to a suicide bomber, Cassidy began experiencing survivor's guilt and blamed herself for their deaths.
- Like McGee, Cassidy wore a watch on her right hand which suggested that she was probably left-handed.
- Is the first and quite possibly only member of NCIS to have originally hailed from Canada.
- Jessica Steen who plays Cassidy also originally played Dr. Elizabeth Weir in the American/Canadian sci-fi show, Stargate SG-1 Season 7 finale episodes, "Lost City Part 1" and "Lost City Part 2" before being replaced by Torri Higginson (Jordan Hampton).