9-1-1 Season 8, Episode 17 saw the hit ABC drama’s core characters moving forward after laying their beloved Captain Bobby Nash (Peter Krause). But in many ways, “Don’t Drink the Water” also served as a trip down memory lane.

From a flashback of Bobby and the team reminiscing over Season 1 emergencies to the return of several guest stars (more on these below), Season 8’s penultimate episode gave fans and characters alike a blast from the past. And one of the most unexpected returns saw Phoebe Neidhardt (Apple Cider Vinegar, Dad, The Rookie: Feds, Station 19) reprising her role as Lorna, a 9-1-1 character who was — and still is — facing some serious dental struggles.

So who is Lorna on 9-1-1? Which episode did Lorna first appear in ahead of Season 8, Episode 17? And what other 9-1-1 guest stars returned in “Don’t Drink the Water”?

From Lorna to Eddie’s Aunt Pepa (Terri Hoyos), Father Brian (Gavin Stenhouse), Graham the cart cop (Sam Roach), and more, here are 9-1-1 Season 8, Episode 17’s unexpected callbacks explained.

Who is Lorna on 9-1-1? Season 8, Episode 17’s Callback Explained

After an earthquake hits Los Angeles, 9-1-1 Season 8, Episode 17 shows the 118 fighting a series of unusual fires caused by a methane leak in the local water supply. Before the team understands the full extent of the situation, however, they’re called to a dentist office where a routine root canal left a dentist burned after his patient breathed fire.

Despite having her mouth full of melted dental blocks, the patient immediately looks familiar to Buck who thinks she could be a celebrity or a woman from his gym. When Hen asks him to grab a blue drape from the counter, however, he remembers how he knows the woman and exclaims, “BLUE! I knew you looked familiar! A couple of Christmases ago, she overdosed on tooth cream.” After the connection sicks in, Chimney exclaims, “THE SMURF!” And 9-1-1 briefly flashes back to the call.

So which 9-1-1 episode is Lorna from? In Season 3, Episode 10, “Christmas Spirit,” we saw her on the phone with her mom denying an invite to Christmas dinner. “It’s not like I can eat anything anyway with this stinkin’ toothache,” she said. “I know it’s Christmas, but I have to work. Give me a break. My mouth is literally killing me.” Lorna explained that she had a double root canal scheduled just in time for New Year’s and hung up on her mom after finding another tube of Benzocaine in her medical cabinet. She squeezed out a large amount of the paste, shoved a glob in her mouth, felt instant relief from her tooth pain, and went to bed. But when she woke in the morning, her skin had turned completely blue. As the show played “Blue Christmas,” Lorna called 911, and Bobby and the team quickly showed up to her door and successfully treated her for hemoglobinemia, brought on by too much tooth cream.

So why bring back Lorna at a time like this? During my 310 rewatch I was reminded that Buck was worried about Bobby dying from radiation exposure back then, and even told him, “You’re an important person in my life, Bobby. One of the most important. I don’t know what I would do if anything were to happen to you.” BRB, SOBBING. The episode also featured one of the greatest family firehouse dinners for Christmas, and 817 opens with Buck flashing back to the days when he, Bobby, and the team would enjoy meals together.

The choice of episode tie back may have been linked to Buck’s nostalgia and emotions surrounding Bobby, but parallels to 9-1-1‘s current depressing reality aside, we know the show loves to bring guest stars back whenever the opportunity presents itself. (Speaking of earthquake episodes, remember when Jeff Pickens (Mike Gray) returned in 9-1-1‘s Season 6 finale?) Once 9-1-1 settled on a dental emergency, the team probably realized Neidhardt was the perfect person for the job. And as we noted above, she wasn’t the only returning guest star of the episode.

9-1-1 Season 8, Episode 17 Took A Trip Down Memory Lane

Before we dive into additional guest stars, let’s remember that Buck opened 817 with a flashback, which showed Bobby reminiscing over two Season 1, Episode 7 “Full Moon (Creepy AF)” emergencies: the team delivering babies in a yoga class, and Buck delivering a tapeworm. Nostalgia was sprinkled through Season 8’s penultimate episode with a callback to Hen and Karen’s wedding, and more, but beyond Neidhardt, some other familiar faces did return.

When Chris (Gavin McHugh) visited from Texas, Eddie’s Aunt Pepa (Terri Hoyos) returned for the first time since Season 6, Episode 14 to have dinner with them and Buck. Earlier in the episode, Buck sought guidance from 9-1-1‘s resident Hot Priest, Father Brian (Gavin Stenhouse), a recurring character introduced in Season 1 who returned earlier this season. And Athena reunited with another familiar Season 8 face, Graham the cart cop (Sam Roach) from Season 8, Episode 8 “Wannabes.”

New episodes of 9-1-1 premiere Thursdays at 8:00 p.m. ET on ABC with next-day streaming on Hulu.