The episode, titled "The Tech Rehearsal", follows the school musical's cast and crew as they struggle to find a new location to test their production, according to Grabeel's exclusive interview with Entertainment Tonight. Reinders gets haunted by her "old demons" in the eerie theater downtown that the choreographer Carlos (Frankie Rodriguez) picked out, and while she lays unconscious, Grabeel creeps into her dreams for an encouraging song-and-dance number titled "Role of a Lifetime" that reminds Reinders' character of her main goal: to inspire her students.
The 35-year-old actor didn't have to think twice about coming back to East High when the opportunity first arose.
"Yes, it was an immediate 'yes'! I was originally called and asked if I was interested in sitting down with [executive producers] Bill Borden and Tim Federle to discuss the opportunity of me being on the show. I immediately said yes, but I was a still a bit hesitant yet intrigued to see how I was going to be used and furthermore, the details of the show," Grabeel told ET. "Once I heard from Tim, passionately describing how he wanted to maintain the integrity of the original movies and music and dancing and spirit and also bring it to the new generation, I became so excited and jumped at the opportunity to be a part of it."
But the character he plays in High School Musical: The Musical: The Series isn't Ryan Evans to a tee: He blended his actual self with Evans to create a more authentic, yet still flamboyant role specific for the TV adaptation of the Disney Channel original movie franchise.
"It was fun to figure out where that line was and how to play myself but with a flair of Ryan," he said. "It was so great to put on my dancing shoes again. I was definitely out of shape because I haven’t danced in so long, but luckily everyone was so nice and helpful and helped this old grandpa get on his feet again."
In another exclusive interview with TV Line, Grabeel talked about the deliberate nods he made to his old role, including his tribute to "We’re All in This Together" from the musical trilogy's first installment. "I also got to wear one of Ryan’s old hats while running around an auditorium, singing and dancing -- which I haven’t done in a long time," he said.
He didn't just dust off his dancing shoes: he warmed up his pipes for his duet with Reinders, whom Grabeel described as "incredibly talented." The two hit it off instantly -- "It felt like we had worked together for many years," he said in the interview -- and he was delighted to know her son was also named Lucas.
"She knows what she's doing!" he teased.
Grabeel isn't the only HSM alum to return to East High. KayCee Stroh, the bookworm-turned-"pop-and-lock-and-jam-and-break"-expert Martha Cox, also starred as a fictional version of herself in the Dec. 13 episode titled "What Team?", according to an ET exclusive interview with the actress. In the show, she drops in at the end of the "Truth, Justice and Songs in Our Key" performance in Stroh's main domain of the cafeteria.
"When I walked back into East High, I was overcome with emotions. So many of my formative years were spent working there in those halls, my big break came over there on that cafeteria table, lots of blood sweat and tears (literally) on that stage!" the 35-year-old star recalled earlier this month. "I actually had to pause and take a moment to collect myself."
Check out Grabeel and Reinders' joint musical number "Role of a Lifetime" below.