Jeff opens the door of the upstairs bathroom and sees nobody in the hallway. He can faintly hear his parents moving about downstairs too. Emily must not be back from her trip yet. Relieved, Jeff walks into Emily's room and hooks up the Chronivac to Emily's computer before booting it up. Might as well have everything set up before she gets home: obviously he's going to have to use the Chronivac on Emily, and maybe the entire family, to get to be her for a while, so he should get his ducks in a row.
Unfortunately, Jeff then heard a car pulling into the driveway. Looking out Emily's window, he saw his sister out of the car, getting her bags out of the trunk. As the car pulled away, Emily began walking inside, and Jeff knew he had to act quickly. The Chronivac had fully booted, so he entered in the relevant info:
SUBJECT: Emily Smith
TRANSFORM INTO: Jeff Smith
START TIME: Immediate
DURATION: Permanent
Was that it? No time to think about it; Emily was walking through the front door. Jeff hit ENTER and hoped for the best.
Almost immediately he heard a scream from downstairs, followed by someone running and stomping up the stairs. Sure enough, it was his old body, in girl's clothes that were now way too close to him. Obviously it was Emily, who naturally ran into her own room in a panic, only to see her own body there, not knowing it was really Jeff. Jeff decided the easiest way to do this would be to trick her.
"Oh my god!" Jeff shrieked in fake surprise. "It happened to you too!"
Seeing Emily continuing to panic, Jeff went on. "I just transformed into your body a couple hours ago. I have no idea what's going on. Do you?"
"No!" shouted Jeff.
"What's that?" came the voice of their mother from downstairs. Jeff knew he had to take command of the situation. He went to the top of the stairway, still in his towel.
"Jeff's back," he said. "He says he went out for a while."
That seemed to satisfy their mom, so Jeff went back into Emily's room to continue the ruse.
"We have to figure this out," he said. "Until then, let's just pretend to be each other."
Emily, in Jeff's body, still seemed confused, so Jeff continued. "Listen, you should probably get out of those clothes," he said, "and into mine."
Emily nodded and walked out of her room. It was still so weird for Jeff to see someone else in his body.
Jeff relaxed. He hadn't realized he was so tense. That was a close one, but he felt like he wasn't out of the woods just yet.