In the upcoming episode of NCIS (9:45pm Sunday on Ten), Abby is reeling from a harrowing attack that killed MI-6 officer Clayton Reeves (Duane Henry) and left her seriously injured.
After waking from a coma and realising Clayton sacrificed his life for her; Abby tells her fellow NCIS team-mates she will take his body to his family in London. And she doesn't intend on returning.
What follows is a heart-wrenching goodbye scene as Abby takes a moment to say goodbye to each of her beloved NCIS team – a team with which Pauley she shared a screen for 15 years.
"Clay died saving my life and I owe him a debt and I intend to see it through," Abby says.
"Clay always wanted to start a charity in honour of his mum. Since he's not here to make that happen, I will. You may not understand, but it's something that I have to do, not just for him but for me."
She continues to say the decision was hard to make, but her gut is telling her to go.
Notably absent from the farewells is Special Agent Gibbs (Mark Harmon). A rumoured feud between Pauley and Mark has meant the two characters have shared next-to-no screen time in the current season – something fans were quick to notice.
And devastatingly, their characters, who won hearts with their special father-daughter relationship, did not reunite for a final on-screen goodbye.
Instead, Abby leaves a letter for Gibbs explaining her decision and why she did not see him before she left.
"Hey Gibbs, you're probably wondering what's with the retro communication," the letter reads.
"Truth is, I chickened out. I was afraid if you asked me to stay, I might waver.
"There's nothing I wouldn't do for you. When I think back on when things in my life got difficult, you were always there to tell me that it would be OK. And it would be because you would make it OK.
"But Gibbs, Reeves is gone and it's not something anyone can fix. Not even you.
"I hope you know what you mean to me. Every moment. Every lesson. Every hug. I'm thankful for it all, no matter what we faced over the years."
The letter almost feels like she is also thanking her co-star Mark for the 15 years they spent together and farewelling their friendship in the process.
Her final episode aired in the States last night and fans and cast-mates were quick to post their tributes.
"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!" Wilmer Valderrama tweets.
"Love you @PauleyP. Thanks for the last decade and a half. Gonna miss you a bunch," Brian Dietzen adds.
Meanwhile, former co-star Michael Weatherly took to Instagram to share his thoughts.
"I will be watching #abby tonight on #ncis and telling my kids,"...it's ok. It's ok." Big kiss!" he writes.
Pauley's departure leaves just two original cast members on NCIS - Gibbs and Ducky (David McCallum). Sean Murray and Brian Dietzen, recurring characters in the early seasons, also remain.
Catch Pauley Perrette's final scenes on Sunday, 13 May at 9:45pm Ten.