By Sandra Gonzalez, CNN

(CNN) -- Warning: This story contains spoilers about the May 8 episode of "NCIS."

The "NCIS" lab has lost its resident goth genius.

Pauley Perrette, who played forensic scientist Abby Sciuto, has signed off from the long-running CBS crime drama after 15 seasons on the show.

Though Perrette's impending exit from the series was announced in October 2017, her character Abby's fate was left in question at the end of last week's episode after she and MI-6 officer Clayton Reeves (played by Duane Henry), were confronted by a gun-wielding thief.

At the start of Tuesday's episode, viewers learned that Abby was in serious condition, having suffered a pierced artery after being shot in the chest.

Reeves, meanwhile, died from his injuries.

Abby's co-workers stayed on the case as she struggled to come out of a coma, figuring out that Abby had been targeted by a person who she helped put behind bars years ago.

When Abby awoke, she helped them crack the case further, leading them directly to the person responsible, a man named Robert King -- an antagonist from a previous season.

After King was back behind bars -- this time sporting a broken nose thanks to the unit's leader Leroy Jethro Gibbs (Mark Harmon) -- Abby told her co-workers she intended leave NCIS to carry through the philanthropic aspirations of Reeves, who died trying to save her.

"Clay died saving my life, and I owe him a debt and I intend to see it through," she said. "Clay always wanted to start a charity in honor of his mom and since he's not here to make that happen, I will. I know you may not understand, but it's something I have to do -- and not just for him but for me."

Gibbs, whom Abby saw as a father figure, was not there for her big announcement, so she told him in a letter.

"I hope you know what you mean to me, Gibbs -- every moment, every lesson, every hug, I'm thankful for it all," she wrote.

After Perrette's exit, the only original cast members who remain are Harmon, David McCallum, Sean Murray, and Brian Dietzen, with the latter two serving in a recurring capacity in the earlier seasons.

Perrette and her co-stars -- both current and former -- marked the character's final episode with a series of tributes on social media.

"Dear Pauley, you were a light and made me feel like family from the first day and everyday for the last two years.. love you sis," wrote Wilmer Valderrama.

"Thanks for the last decade and a half," added Brian Dietzen. "Gonna miss you a bunch."

Perrette's closing thoughts seem best summed up by her character, who told her co-workers, "you have to go with your gut, and my gut is telling me I have to go."