Once William finished nursing his second glass of water, Buffy and Giles helped him to the bedroom, so he could rest more comfortably.  Buffy chose to stay while Giles returned downstairs.
 
Over the next hour, the room remained quiet over-all, with the exception of several occasions when a semi-conscious, restless William murmured incoherently before calming and returning to sleep.
 
With each instance, Buffy’s concern intensified, until she could no longer stand the waiting.  Not wanting to disturb the finally settled William, she slowly stood from her spot of vigil on the edge of the bed and headed downstairs.  All the Scoobies were still in full research mode, and no one noticed her presence until she interrupted.
 
“Please tell me you guys have found something—anything.”  Buffy’s uneasiness caused her voice to tremble slightly.
 
“I found several shape-shifting spells that require the caster to obtain a personal item from the victim.  But since you were Toth’s target, and Spike was affected, those were a big no-go,” Willow sigh dejectedly.
 
“Sorry Buff, we’ve got nada here too.  How’s William holding up?” Xander gave Buffy a half-hearted smile in hopes she would take some solace in their efforts, despite their lack of success.
 
“He’s resting comfortably for now.  Thanks for working overtime on this, guys.  Okay, if there’s nothing else to report, I’m going to head back.  Just let me know if you—” Buffy was cutoff mid sentence by Giles’ unexpected utterance.
 
“Oh dear Lord!”
 
“You know, I really hate it when he says that,” Buffy groused as she mentally prepared herself for Giles’ findings.
 
“Ferula-gemina.”
 
“Bless you,” Xander joked, attempting to lighten the ominous feeling that quickly descended upon the room.
 
“Very droll, Xander.  As I was saying, Toth’s rod device, it's called a Ferula-gemina.  It splits one person in half, distilling personality traits into two separate bodies.  As near as I can tell, Toth was attempting to split the Slayer into two different entities.”
 
“Two Buffys?”  Xander shifted on the couch, moved the sizeable book from his lap, and placed it on the coffee table.
 
“Yes, one of them with all the qualities inherent of Buffy Summers.  The other would have everything that belongs to the Slayer alone: the strength and speed, the heritage.  When it hit Spike, I think it separated him into his strongest qualities, those belonging to the demon, and his weakest, those belonging to the human.”
 
“But which is the real one?”  Buffy’s expression was one of utter bewilderment.
 
“They're both real. They're both Spike.  There's nothing in either of them that he didn't already possess.”  Giles nodded his head in affirmation.
 
“I still don't get the original plan. Why do it?  The Slayer half would be like Slayer-concentrate.  Pretty unkillable.”  Willow ’s brow scrunched in confusion as she moved closer to Giles.
 
“But the two halves can't exist without the other.  Kill the weaker Buffy half, and the Slayer half dies.”  Giles gaze moved steadily over the group, appearing to be gauging everyone’s reaction.  
 
“So, same thing for the Spikes, right?  Both of them need to stay alive, or they both die.”
 
When Buffy spoke this dismal possibility out loud, it made it all the more real.  Overwhelmed by this knowledge, Buffy began pacing when the uneasiness returned with full force.  However, she remained in motion to prevent the others from seeing her fighting newly formed tears.
 
“I believe so, Buffy.  It appears his demon and human have an undeniable obligate symbiotic relationship,” Giles clarified.
 
Buffy stopped in mid-stride and turned toward her Watcher.  “What in the huh?  What’s an oblique cymbal relationship?”
 
“Obligate symbiotic relationship is a phenomenon in nature in which two organisms cannot survive without the other.  It is a precarious balance, to say the least.  If one falters or dies, the other will surely follow closely behind.”  Giles removed his glasses and gently cleaned the lenses, then returned them to their rightful place.
 
“Oh!  It’s like the relationship between Marine worms and Archaea bacteria found near the hydrothermal vents on the Mid-Oceanic Ridges,” Willow added excitedly, as the others eyed her with perplexed amazement.

The animated redhead noticeably deflated after her gaze darted around the suddenly silent group. 

“What?  Unlike some of us, I paid attention in Dr. Gregory’s class.  Might I add, I always did the extra credit assignments, too.”
 
“Who’s Dr. Gregory?”  Xander’s brow creased in obvious confusion.  He appeared to be sorting through his sketchy memories of all things high school that were learning related.
 
“You don’t remember our biology teacher from sophomore year?  Well, he was our teacher until Miss French ate his head.  Then She-Mantis became our substitute and started collecting virgins to fertilize her clutch of demon-spawn-eggs?  Ringing any bells, Xander?”
 
Willow smirked while she watched Xander’s eyes widen when he recalled whom she was talking about.  Quickly, he attempted to change the subject before his astute girlfriend chimed in.
 
“So Giles, is this two-Spike problem an easy fix?”
 
“I’m not quite sure, Xander.  To know for certain, it will require more research.”  Giles laid the helpful tome on his desk, picked up another hefty volume, and started leafing through the weathered pages.
 
“Okay, we know the reason for two Spikes, which thankfully rules out one of them actually being Toth.  So our next step is hitting the books—again.  This time, we need to figure out what’s going on with William, especially when the demon appeared fine, even after Riley shot him.”  Buffy looked imploringly toward her friends and Watcher, hoping they would find the reason and soon.
 
As if Buffy’s words were their starting gun, each Scooby was set into motion.  Giles returned to the bookshelf, and Xander and Anya started compiling the collection of books surrounding them in order to make room for more.
 
However, it was Willow’s thousand-yard-stare that caught Buffy’s attention.  Before she could comment on it, Buffy watched a sudden awareness emerging across her friend’s features.
 
“We don’t need books for this guys.  All we need is my laptop.”  Willow hurried over to her bag propped against the couch.  She carefully removed her laptop and set it down on the surface, while she sat down at the desk.
 
The recognizable whirling of the computer coming to life and Willow’s agile fingers hurrying across the keyboard drew everyone’s attention, as they formed an attentive, half circle around the redhead.
 
“Thanks again to Dr. Gregory’s class, I know where to look to figure out what’s happening to William.  For the first time in Hellmouth history, this is not magic related.  What I think William has is simply because he’s human.”
 
With a few more keystrokes, a self-help medical website popped up on the screen.  Willow moved the mouse and with one click, a small androgynous figure appeared along side a list of symptoms.
 
“The age I picked for William was how old I assumed he would have been when he was turned.  I didn’t think an over-century-old, no-longer-vampire really fit the sixty-five-plus age bracket.”

She scrolled down the list, clicking on William’s ailments.  “Okay, he’s showing signs of dizziness, dry skin, fatigue, increased thirst—”
 
Willow continued adding to the list.  Each symptom weeded out possible diagnoses, until one unmistakable explanation appeared at the top: dehydration.
 
“This is it.  This is what’s going on with William.”  Willow pointed to the diagnosis highlighted on the screen and looked back at the others to judge their reactions.
 
Buffy leaned forward as if this would help the information make more sense.  “Dehydration?  I don’t get it.  I’ve seen William drink, we all have.”
 
“Of course!”  Giles exclaimed, his hands rising in the air in sync with his words.
 
“Let me add to the record.  I’m not too fond of that remark either,” Buffy grumbled while she leaned back, her gaze moving to her Watcher.
 
“The cause of William’s symptoms is a direct link between the two sides.  Buffy, the demon side you came across, it still possessed an active chip, correct?”  The lines of thought formed on Giles’ brow, when the pieces of the puzzle came together in his mind.
 
“Yeah, all in its nose bleeding glory, but what does—” Buffy’s eyes widened when she finally caught on.  “The chip.  The chip’s preventing Spike’s demon from feeding off humans.  Since I highly doubt he’s been bagging it, and after being injured—”
 
“The deterioration of William’s health has been accelerated from the combination of blood loss and minimal feeding by the demon.  I’d venture the demon is showing signs as well, but it would not be as severe as William’s.”
 
Giles removed his glasses again.  Buffy watched him sweeping the every-ready cloth across the lenses in methodical circles.  Each stroke appeared to increase in pressure and speed.
 
“So let me get this straight, William is starving to death ‘cause the demon hasn’t been feeding?”  Buffy broke her gaze from Giles’ hands and rose to his eyes.  She could see his growing concern for William mirroring back.
 
“Buffy, William isn’t starving, he’s dehydrated.  They’re different.  But unfortunately the outcome, if not treated, is the same.  It’s just dehydration…well…it happens a lot faster than starvation.”  As Willow continued to speak, her voice softened, and by the end, it became difficult to hear her.
 
“So tell me straight, how long does he have?”  Buffy shifted into Slayer mode, since she felt the woman inside being crippled with worry.
 
“I think I can answer that from when I was Army-guy.  I remember a simple survival rule of thumb: three hours without shelter, three days without water, three weeks without food.”  Buffy sensed Xander’s apprehension while he gave her this difficult news.
 
“Three days?  William’s already burned through two, and at the rate he seems to be going downhill, I don’t think—”
 
Buffy couldn’t bear finishing her thought.  She felt her chest tightening and fresh tears forming.  After a quick intake of breath, attempting to steady herself, she reached deep within and pulled forward the inner strength she relied on when things felt they were beyond all hope.
 
“Okay, here’s the plan.  Giles and Anya, you stay here and take care of William.  Take turns, while one of you keeps an eye on him, the other is looking for ways to maybe slowing this thing down.  Xander and Willow, you’re coming with me.  We only have a few hours left before sun-up.”  Buffy walked over to Giles’ weapon chest, lifted the lid, and started searching.
 
“Giles, what’s with the minimal weaponage?”  Buffy’s voice sounded slightly muffled from her position leaning over the chest.
 
“Well, with my recent purchase of the Magic Box, I felt there could be our newest, if you will, headquarters.  Also, with the rather unappealing demises of previous shop proprietors, and myself already having been accosted, I decided to move a great deal of my collection there.”  Giles explanation prompted Buffy to close the lid, while her mind started recalculating her strategy.   
 
“What’s the plan, Buff?”  Despite Xander’s question, he and Willow had dutifully collected their jackets and were readying themselves to go.
 
“Okay, first we hit the Magic Box.  There’s a certain oldie-but-goodie we need that can incapacitate the demon without harming William or Spike.”
 
She watched Willow nod and Xander knowingly smirk in response.  Buffy knew full-well they understood what she had in mind and were already onboard with the unspoken means of capturing the demon.
 
“And once we have what we need—we’re bringing back a demon,” Buffy announced confidently, while sliding her arms into her jacket before heading toward the door with Xander and Willow in tow.
 

 
 
Author’s Notes:

Big thanks to my lovely betas: Sanityfair and Diebirchen
 
Some of the dialog was taken directly from ”Replacements,” written by Jane Espenson.  I did have to tweak some of it to make it fit into my story. http://en.wikipedia.org/wiki/The_Replacement
 
Obligate symbiotic relationship: http://en.wikipedia.org/wiki/Symbiosis
 
Marine worms, Archaea bacteria, and hydrothermal vents: http://marinelife.about.com/od/habitatprofiles/p/vents.htm
 
Season One, episode 5, ”Teacher’s Pet”: Dr. Gregory was the biology teacher before She-Mantis killed him. http://en.wikipedia.org/wiki/Teacher's_Pet_(Buffy_the_Vampire_Slayer)
 
Surviving without water: http://ask.metafilter.com/41162/How-long-can-humans-last-without-water