Frisk got out of sight easily.
The only obstacle he faced once off-stage was the fire man stage manager who asked him where he was going. Once Frisk told his lie, he let him go and warned him about getting his mic wet in the bathroom.
After that, Frisk ran straight for the backstairs still carrying the water bottle in one hand and removing his mic with the other. Just as he reached the stairs, he threw the lavalier mic on the floor and bolted through the door as fast as his little legs would carry him.
Frisk felt his frightened tears running down his face and blinding his vision, but he didn't dare stop lest Mettaton seize the opportunity to drag him back. He wished his determination was healed so that he could make himself run faster. He wished he had known better than to agree to any of this. More than anything else, he wished his new family was right there to encourage him.
As if an answer to prayer, Frisk felt his phone vibrating. He stopped to catch his breath and look at it. It was Sans.
Without hesitation, Frisk answered the phone and said, "Sans?"
"Kid, I watched the show," Sans said from the other end. "Where the hell are you right now?!"
"I'm going down the backstairs," Frisk said between breaths. "Mettaton doesn't know I'm gone yet. I'm meeting Papyrus and Undyne outside by a boat."
"Then, why are you still in there? Move your ass now!" Sans yelled.
"Okay," Frisk said nervously resuming his quick pace down the stairs.
"Frisk, what were you thinking?! For God's sake, you remember what has happened every single time you have faced that freak! What possessed you to go along with his crap this time?!"
"I'm sorry! He said he would give me money!"
"You did all this just to have some extra spending money?"
"It wasn't for me! It was for you and Papyrus!"
Sans went silent on the other end for a moment before he responded in a gentler tone, "What? Why were you trying to get us money?"
"I wanted to help you guys out," Frisk responded sadly slowing down just as he was getting close to the back exit. "Mettaton said that you guys needed money to take care of me and that I'd be able to make it easier on you, so I thought that if I did what he said and got us money then I could help you out and not be so useless. I mean you guys have done so much for me, and there's nothing I can do to pay you back. I can't break the barrier or set you free, so I thought the least I could do was make you richer so that you could be happy down here."
On Sans' end, the phone was on speaker so Toriel could hear. She looked up from her paperwork to see a terrible sight. Both Sans' eyes were glowing bright blue and his free hand was rolled up in a fist. He was furious.
"Sans?" Frisk asked nervously as he cautiously walked through the back door.
"Frisk, you didn't have to do that for us," Sans replied in an astonishingly calm tone. "We're family. We'd never ask you to sell yourself out for us. We're the legal guardians and big brothers. We're the ones who're supposed to figure out money, not you. Understood, kiddo?"
"Yes, I'm sorry," Frisk said quietly while powerwalking to the boathouse.
"Another thing, you ain't useless," Sans said. "Stop saying you are. Are you on the boat yet?"
"Yeah," Frisk said stepping into the boathouse and immediately being scooped up by Papyrus.
"Oh, Frisk! Thank God!" Papyrus said holding him tightly against his armor. "I thought we lost you. Who are you talking to?"
"Sans," Frisk said trying to squirm out. "Papyrus, put me down!"
"Shut up and let me talk to him," Undyne said snatching the phone away from Frisk and holding the receiver next to her ear. "Sans, it's me. We got him. What do you want us to do? What? Okay…okay…yeah, sure…We'll go straight there. See you soon."
Undyne handed the phone back to Frisk, hopped on the Ferryman's boat, and said, "Get your asses on board now. We're heading to the Ruins."
"Why are we going there?" Papyrus asked as he hopped on with Frisk still in his arms.
"That's where Toriel is," Undyne replied picking up the oar and using her magic to command the boat to move. "Never met her, but she's a friend of Sans' and is evidently Frisk's fourth legal guardian, so I trust her. Now, sit tight. With this boat, it shouldn't be long."
"Anything else?" Frisk said as the boat got going.
"Yeah, you're grounded for another week," Undyne said.
"Dammit," Frisk mumbled under his breath.
The boat quickly galloped around the bend. They were just in time.
Back in the studio, Mettaton was still basking in the applause of his audience and the attention of his paparazzi when one of the photographers asked, "How about we get a picture of you and your new son?"
"That sounds like a great idea," Mettaton said before calling to his child. "Frisk, dear, could you come here for a moment?"
"Hey! He's not here!" another photographer yelled.
Mettaton turned around quickly to see that Frisk was not on the couch where he was before.
"Oh, dear," Mettaton said successfully hiding the flutter of panic running through his circuits. "Would you give me a moment?"
Mettaton cleared a path through the paparazzi, stepped onto the stage, walked backstage, pulled his stage manager aside, and asked, "Have you seen Frisk?"
"He said he was going to the bathroom, but that was about fifteen minutes ago," he said. "Maybe one of us should check to make sure he's alright."
Mettaton's eyes narrowed in suspicion. He peaked out behind the curtain and saw that neither Undyne or Papyrus were at their seats, and his heart began to race.
"Shit," Mettaton said quietly to himself before stepping on-stage and announcing, "My lovely audience, I hate to be the bearer of bad news, but we are having some technical difficulties and have to go into an hour-long intermission. Don't worry. We'll be back as soon as we can. In the meantime, enjoy some refreshments and merchandise in the lobby."
Mettaton went back behind the curtain while tensing up at their disappointed groans.
"Mettaton, what is the matter?" his stage manager asked.
"My son's friends aren't in the audience anymore. That means they ran away together," Mettaton said allowing the tension to show in his voice.
"Are you sure?"
"Yes, I had to physically push them out just to get them to leave me and the human alone for a few hours. They wouldn't leave without him willingly. I thought I prepared for every possibility. I fully expected his 'family' to be upset about the adoption announcement and try to fight me for him, but I didn't expect my son to react so quickly. The boy is more resourceful than I thought."
"Okay, this is bad. Do you think we should call the royal guard? This is technically kidnapping. Isn't it?"
"Undyne is the captain of the royal guard. I couldn't bribe one of her underlings to cross her. They're too loyal."
"Then, what do we do?"
A smile came across Mettaton's face as an idea crossed his mind and he said, "You're going to make sure my audience has enough nourishment and merchandise to keep their lovely hearts' content. I have a plan. I'm going to get my son back myself."
"Sir," the stage manager said as Mettaton turned around and started to walk away. "Undyne is really strong. Her friend looked strong, too. How are you going to stop them?"
"My dear Inferno, this is Mettaton you're talking to," Mettaton said posing dramatically and confidently. "There's nothing I can't handle with style and a smile. I love that. Please make a note to put it on some merch later. I've gotta go."
Mettaton winked and walked away leaving Inferno to take care of the studio while he tracked down his son. He walked the hallways looking for any trace of his child as he headed towards where he suspected Frisk headed to.
As Mettaton approached the back stairs, he saw Frisk's microphone thrown haphazardly on the floor. He smiled and stomped his foot on the floor to make his magic portal to the boathouse.
Mettaton then jumped through the hole and shut it behind him. As he looked around the boathouse, he saw with little surprise that the trio had already left.
In response, Mettaton walked to the edge of the dock, looked out across the water, picked up his phone, and made a phone call to an employee at the casino in the city.