The Phantom Limb by William Sleator, Ann Monticone

“We were expecting you, tool,” Destiny said with a smirk.
    â€œDon’t you have a life?” DCynthia said, but she hada guilty expression as she said it. At least her voice was soft, not braying. They both had to be careful that the staff didn’t hear them taunt a visitor.
    â€œWhy did you think Matt would ever help someone like
you
?” Destiny asked. She put her hand over her mouth and giggled. DCynthia looked away. When Destiny got her laughter under control, she continued smugly, “We told him to shut up about you. And it worked.”
    Isaac had to fight the urge to smack her. It had been a vain hope to think he could get them on his side, but he had to try one more time. “What about Dr. Ciano?” he said. “What do you think of
her
?”
    â€œWe know how to play everybody here so we get what we want, not like the other candy stripers. The staff gives us the easiest jobs, like sitting here and checking in guests. We’ve talked to some of the other candy stripers. They’re always running around getting exhausted.
That’s
not for
us
! We’re getting out of here as soon as our time is up.
Hasta la vista
.”
    He sighed and gave up. “Gotta go check on—”
    â€œYour
mommy
!” Destiny mocked him.
    Candi was at the nurses’ station. “I’m afraid your mother won’t have much to say to you today, dear,”she said pleasantly. She clucked her teeth and shook her head. “I have to tell you that the doctor’s very worried about her.”
    He wanted to say,
None of you seem worried about her.
Instead, he controlled himself and said determinedly, “I need to see her.”
    â€œI’m afraid you can’t,” Candi replied. She smiled at him. “She’s going to have a procedure in the basement soon.”
    He felt scared, but he was determined to fight back. “It’ll just be for a minute. OK?”
    Candi’s voice had a steely edge to it. “Well, all right. You can open the door and peek in for a few seconds.”
    As he feared, Vera was unconscious. The bandage on her arm was even larger than before. Her body seemed almost lifeless. There was no more time.
    Isaac rushed home and immediately got out the mirror box. He needed the phantom limb’s help before it was too late.
    The phantom limb slid into the mirror. It was holding up three fingers again. Was it really trying to say “triad,” as Grandpa had suggested? Isaac knew he had to search the net to find out what Joey was trying to tell him.
    Grandpa had known only two meanings for the word, the musical term and the group of three people. How could he find out if it had any other meaning?
    He went downstairs and found Grandpa reading. He asked him about the term “triad” for the second time. After thinking about it, Grandpa said, “If it refers to that doctor, maybe it has something to do with psychology.”
    Isaac went back upstairs, opened his computer, and went to Google. He typed in “triad and psychology.” Several entries appeared with the title “Macdonald Triad.”
    â€œYes!” Isaac said to himself. He’d found it!
    â€œThe triad” referred to three childhood behaviors that were often displayed by children with psychopathic tendencies who were prone to becoming serial killers. Most kids with one, or even two, of these behaviors never became a serial killer. But almost every serial killer who had ever been studied possessed all three. One trait was cruelty to animals or other small creatures—like the way the girl in the mirror treated her dolls. Another trait was enuresis, or bed-wetting, which was why the other girls in the cabin had made fun of her. The third trait was arson, the deliberate starting of fires. If Isaachad ever seen someone look happy, it was when that girl was preparing to burn down the cabin—with the other girls in it.
    He went over to the