Unbeknownst to Dan, Kenna was a villainess and serial killer, having killed nine victims in a six year span between 2005 and 2011. She gained the nickname, "The Dentist," due to the fact that she would remove a tooth from each of her victims as a trophy, and regarding her method of murder, Kenna had been known to shoot, stab, and strangle her victims to death. After her last kill in September 2011, Kenna settled down and married Dan, and they had children together at that same time.
One of Kenna's nine victims was revealed to be a woman named Pamela Calweiler, who was Mooney's cousin. Pamela's murder led him to begin writing a book on The Dentist, and it was after the ninth and final murder that he suspected a man named Lewis Dacey of being the serial killer. However, Mooney called Dacey some time before his death to apologize, as he had broken into the Reynolds household and found a box of the victims' teeth, meaning that he was closing in on Kenna's true identity. Knowing that Mooney had taken her box and realizing that he could expose her secret, Kenna turned heel again and stabbed Mooney to death in his hot tub, using a box cutter to commit the murder before taking back her possession.
After the box of victims' teeth were found in the Reynolds' home, Dan was suspected and subjected to Leroy Jethro Gibbs' intense interrogation. However, Kenna ended up revealed as the villainess when her purple nail polish was found on the box, and that led to Gibbs and Jackie Sloane encountering Kenna at her garage. The villainess snarled at the pair over her husband behind held at NCIS, but after the pair outed her as The Dentist and as Mooney's killer, Kenna confessed. In addition, the evil Kenna stated that Mooney was going to ruin the good life she had, while also claiming that she was past her actions as a serial killer. Gibbs handcuffed and arrested Kenna following her reveal and confession. A motive was never revealed for Kenna's actions as The Dentist, and NCIS was left wondering how Dan never knew about Kenna's heel persona.
- Lise Simms also appeared as the evil Wendy Johnson on Castle.
- Kenna Reynolds is similar to fellow NCIS villainess Karen Bright, as both were deranged serial killers who also collected trophies after each kill. In addition, both married men who had no idea of their wives' villainous actions, though one difference was that Karen killed her husband in an attempt to set him up, while Kenna continued her marriage but killed another victim to prevent her secret from being uncovered.
- "He was gonna ruin everything. I got past all that a long time ago. I have everything I need now: a great husband and beautiful kids. (Sloane: "And some really bad old habits.") I was living a really good life here...until that reporter found me! I just couldn't let him take it away." (Kenna Reynolds revealing why she killed Derek Mooney, as well as revealing her past as a serial killer)