The ambient splashing that was ubiquitous to all caverns in Waterfall blended with the dripping noises emanating from Sixbones's appendages.
"Come on, buddy," Undyne coaxed the Skelebros out the front door. "I'll give you a Bisicle when we get there, okay?"
"Kaaaaaaay," both heads said simultaneously, their words echoing more than normal in the open cavern.
Undyne took Papyrus's hand as she kicked the door closed behind her, ignoring the sticky goop coating her scales. They left a trail of oozing fluid wherever they went, but it evaporated quickly without leaving a trace. Undyne had been worried for the first few days that they would ooze themselves out of existence, but they seemed to have an endless supply.
Casting a quick glance around for any bystanders, Undyne led the creature down to the ferry station, their movements limited to their top speed of a slow shamble. Undyne had seen them move quickly on occasion, especially when they felt themselves or Undyne were in danger, but for the most part they couldn't be prodded to move any faster than a ponderous shuffling.
The boatman turned his hooded head to observe his new passengers impassively. Without a visible face, Undyne couldn't discern his reaction to Sixbones. There was a reason she didn't take the monster out in public very frequently, but the boatman didn't seem to care that an abomination of nature was slowly clambering onto his boat. Undyne hopped lightly onto the back of the boat, prepared to steady them all should Sans and Papyrus suddenly get it into their heads to try walking away or some such nonsense.
The creature half-turned so Papyrus's head could smile at her. Undyne's heart twisted as she tried to force down the awful memory of the first time she'd seen her former friends this way.
Alphys heard the pounding at the door. There was only one person she knew who could produce such earth-shaking noises.
"Open up, Alphys! For God's sake, Al, open the door! I know you're in there!" Undyne roared. "You can't hide in there forever! Just come out and talk to me!"
Alphys's claws hesitated over the intercom. There was nothing she could think of to say to her friend. No excuses for what she'd done, no explanation beyond the obvious, no forgiveness that could be asked or offered. The only thing she could do was continue to hide and pretend the outside world didn't exist.
Unfortunately, the outside world was currently threatening to break her door down.
"Alphys!" Undyne shouted, her voice tinged with desperation. "Whatever's happening, you can tell me. You know I've got your back no matter what, right? Just talk to me, please! Tell me what's going on! Why haven't you come out of your lab in weeks? Where are Sans and Papyrus?"
The reptilian scientist was crying now, hiding her face behind her claws as though that would make a difference. She knew that it was the end of the line, that there would be no stopping Undyne from bursting in and discovering Alphys's crimes. She knew that there was nothing to be gained by postponing the inevitable anymore, but she found herself unable to move. Panic gripped her muscles, preventing her from opening the door or answering Undyne's urgent hollering.
Undyne's pounding renewed itself, the entire building shuddering with the impact. Alphys shook herself out of her fear-induced immobility, knowing that Undyne was more than capable of smashing a hole in the building if she was sufficiently motivated.
And right now, she was more than sufficiently motivated.
The door slid open with a 'whoosh.' Undyne stood outside with her fists raised to assault the door again, her helmetless face twisted with fury.
"U-undyne!" Alphys squeaked breathlessly, unable to repress the reflex to pretend everything was normal. "Wh-what brings you here? Would you l-like some tea? You m-must be overheated after-"
"Stuff your tea, Al," Undyne growled, elbowing past her into the lab. "Where are they?"
Lies. So many lies. Lying had become so much a part of Alphys's life, she found herself unable to stop now. "I d-don't know..."
Undyne shot her a furious glare before vanishing into the back room. Alphys heard the noises of Undyne tearing apart the lab, opening doors and overturning furniture in a vain search for her friends.
"Please stop! Undyne, th-this is pointless," Alphys implored, wringing her claws nervously in the doorway as Undyne destroyed Alphys's living room. "Th-they're not here."
Undyne whirled to face Alphys, as angry as ever but with tears in her eyes. "Then WHERE ARE THEY?" she demanded. "Where- where's Papyrus?" Her voice broke.
Alphys stared at her for the longest moment, feeling panic beginning to freeze her again. It was time for her sins to be brought to light.
"C-come with me."
They didn't speak on the elevator ride. They stood next to each other in tense silence, Undyne's heart racing with frightened anticipation and Alphys drowning in sick dread.
Undyne flinched as the elevator dinged. The doors opened to a lab underneath a lab, with a jarringly different ambiance to Alphys's public work area. The place positively radiated death, the seeping fog and unnatural chill giving the darkened laboratory the aura of a tomb. How was it even possible for a location in Hotland to be this cold? Undyne shivered.
"Al... what is this?" her voice echoed emptily, so unlike the bubbly reverberations of Waterfall's echoes.
"This is the True Lab," Alphys said forlornly. "They're down here."
"Hot damn! Why didn't you say so?" Undyne's face regained some of its color, shifting from horror to anticipation. "Hey, Papyrus! Sans! Olly-olly-oxen-free!"
"Undyne, wait-" Alphys stretched out her claw, but Undyne had already bounded forward. She disappeared around the corner before Alphys could move to stop her. As Alphys hustled to catch up to her long-legged friend, she heard the footsteps ahead of her abruptly stop.
"Hey, who's there?" Undyne's voice stuttered. "Wait, what-"
Alphys hadn't quite reached Undyne when she heard a blood-curdling shriek pierce the oppressive stillness of the True Lab. By the time Alphys had rounded the corner, Undyne had backed up as far as she was able from the horrifying monster that was all that remained of her skeleton friends.
"Undyne, please! I c-can explain!" Alphys stammered, quickly moving to put herself between the panicked Undyne and the confused amalgam before someone got hurt.
"Alphys-" Undyne choked, her face frozen in horror. "What- what is that thing?"
The creature tilted its heads at Undyne. "Neeeeew... friiiiend?" it asked with Papyrus's mouth. Undyne made a disgusted choking noise.
Alphys hadn't noticed when she'd started crying. "Undyne," she whispered. She felt like her SOUL had been sucked away, leaving nothing but a broken husk of lies and unethical science experiments. "I'm so sorry, Undyne. I- I didn't mean for any of this to happen."
"What is it, Al?" Undyne asked again, lowering her voice to match Alphys's. "What happened here?"
Alphys shook her head, utterly defeated. "Go back upstairs, Undyne. I'll explain e-everything, but I don't want to stay down here any longer."
The boat came to a gentle stop at the Hotland station. Undyne paid the ferryman, adding an unnecessary tip for his trouble, and helped the Skelebros off the boat. They looked around with interest, unused to any scenery besides the True Lab and the cavern that housed Undyne's residence.
Keeping a firm grip on the bros' arm to prevent them from wandering off or teleporting away, Undyne led them up the stairs to Alphys's lab. They hadn't been here since Undyne had adopted them, removing them from their lonely environment to take them in at her own home. After she'd had time to wrap her mind around the tragedy and gained the perspective to be back on speaking terms with Alphys, Undyne had begun visiting Sixbones on a regular basis. The poor creature was desperate for companionship, and it had latched (literally and figuratively) onto Undyne like a child. Eventually, compassion and guilt had driven Undyne to forcibly remove Sixbones from Alphys's inadequate care and into an environment where the poor thing could receive more attention.
It had taken them both some time to get used to the arrangement. Undyne had finally stopped summoning her spears every time the creature suddenly teleported into her peripheral vision, and had become accustomed to its attempts to help her make spaghetti. She even began to enjoy the delighted expression on Sans's face (and the exasperated expression on Paps) when she forced a fake laugh at his garbled jokes. Perhaps the most heartbreaking attribute of the monstrosity was when it expressed some limited form of understanding that they had, in fact, once been two separate beings. In their quiet moments, Undyne had caught them holding hands or asking incoherent questions to the other head.
God, she missed Papyrus so much it hurt. As tenderly as she cared for the creature they had become, it was a constant reminder of the lively skeleton who had filled her life with so much joy. And try as she might, despite knowing that this was never an intended consequence, she found herself unable to completely forgive Alphys for what she had done.
Undyne kept her expression carefully neutral as Alphys opened the door to allow them all access into the True Lab. The barest pleasantries were exchanged, any pretense of friendship undercut by the tension of knowing what was about to happen.
"Sit here, buddy," Undyne said gently, gesturing to one of the empty beds. "Just hold still for a while, there's a good boy."
Sans's head glared at her skeptically. "Biiiisss..."
"That's right, I promised you a Bisicle, didn't I," Undyne remembered. "Leave it to you to hold me to that, Sans."
"I-I've got a few upstairs," Alphys offered. "Wait here for just a few seconds."
Sixbones waved a melancholy goodbye as Alphys hurried back out of the room. Undyne was left alone with her thoughts, which was not a good place to be at the moment.
Am I doing the right thing? she wondered doubtfully, watching the amalgam sitting patiently on the bed. They seem pretty content this way... Is this me being selfish? Risking their lives for the chance to see Papyrus again? Would leaving them like this really be too bad?
She knew there weren't many choices. Racked with guilt and grief, Undyne had tried to put them out of their misery in a moment of weakness. Her spears had passed right through, scrambling the creature's HP bar and dialogue box but leaving it otherwise unaffected. Alphys had told her later that there was no way she'd yet found to kill any of the Amalgamates. They were stuck, not truly sentient nor fully dead, shambling for eternity in an oozing twilit hell.
Alphys's arrival interrupted Undyne's brooding. She handed the bros a Bisicle, which they immediately split, and offered a second one to Undyne. She declined with a brief head shake, and Alphys kept it for herself.
"Um, b-before we start," Alphys began nervously. "There are a lot of preliminary tests to be done, to f-find out if this is even possible at all, but... I h-have to know. I can't ask them for th-their consent, so I have to ask you. Are you really okay with th-this? Are you willing to take responsibility f-for any possible outcomes?"
Giving Papyrus's empty eyes one last lingering stare, Undyne nodded gravely.
"Let's do this."