Prescott wasn’t surprised by Holly’s message. He’d assumed an investigation committee would be skeptical of Holly’s story, although it might hold up if she kept her cool. But no need to find out.

He packed a tote bag with preparations for his visit, including a letter on official Institute stationery offering her a job in his lab and a bottle of full-bodied red wine. The neighborhood was quiet when he left his condominium at nine and he took even more care than usual going to Holly’s apartment, walking the three miles from Cambridge to Brookline. He kept the hood of his jacket up and was confident that he hadn’t been observed when he arrived a little before ten.

Holly buzzed him in and he used a handkerchief to open the door. She was sitting on the couch with a glass of wine in front of her.

“How are you doing?” he asked. “Sounds like things went pretty much according to plan with the committee, although I’m sure it was a tough session for you.”

“It was a bit rough,” she said. “They don’t entirely believe me, but I can tell they’re intrigued by the story. It’ll help when they check Pam’s travel schedule, so I’m pretty sure I’ll be able to pull it off.”

“Good work. Well, the time’s finally come.” He reached into the tote bag and pulled out the letter. “Here’s your offer letter, with a start date the first of next month. You’ll get official administrative paperwork next week.”

She read it quickly and smiled. “Perfect. Institute for Advanced Neuroscience, here I come!”

Then she handed him a piece of paper. “And here’s what you’ve been waiting for. The real 40492. You can order some and get the experiments started even before I make the move across the river.”

He scanned the paper. A printout from a major chemical company with the compound’s structural formula, ordering information, and a summary of its activities as an anticancer drug. Finally. Everything I need.

“Excellent,” he said. “We’re good to go. Now how about a little celebration? I brought a special bottle of wine for the occasion. A hearty Spanish red.”

“Great, I’ll get us some glasses.”

“No, you just relax. You’ve had a tough day. I’ll take care of it.”

He took the wine into her kitchen, where he put on latex gloves he’d brought from the lab, opened the bottle, and poured two glasses. Then he added the contents of a vial in his pocket to one of them. Nembutal, the drug commonly used in labs for rodent euthanasia. And for capital punishment and physician-assisted suicide. The vial was a standard veterinary preparation from his lab supply, which he’d confirmed from Pam’s paper was the same as they used in her lab. So it would have been equally easy for Holly to take some home.

He took off the gloves, brought the glasses back to the couch, and sat next to Holly. “To my new favorite colleague.”

They clinked glasses and drank.

His head started pounding as he watched her take her first swallow. Murder. I can’t do this. She has to drink about half the glass, there’s still time to stop her.

Holly raised her glass again. “And to the real 40492.”

He started to grab her glass. But then he got control of himself. There’s no choice.

“I’ll drink to that,” he said.

They both drank deeply and Prescott raised his glass again. “And to the end of Pam Weller.”

“Amen to that,” Holly said as she took another long drink.

He started to tremble as he watched. Half the glass gone now. It was done. Maybe another fifteen minutes or so for it to act. Maybe less.

She turned to him. “Are you alright? You look pale.”

He had to catch his breath. “Sure, I’m fine. Just thinking about experiments with the drug.”

She raised her glass again, her hand starting to tremble. “To our drug.”

Her words began to slur.

Then she slumped back on the couch and seemed to go to sleep.

Prescott recoiled, eyes wide. It’s happening.

Her breathing slowed.

And stopped.

A chill came over him as he watched the life leave her body. The bile rose in his throat and he ran to the bathroom to vomit.

The room was reeling when he staggered back into the living room. Keep it together. She had to die. She was a weak link. Keeping her around would be too risky.

At least it was a peaceful death. Like the mice.

Time to finish up.

He put the gloves back on and started his cleanup. First he found her disposable phone in the kitchen and put it in his tote bag. Then he took the glass Holly had been using before he came, dumped out the wine that was in it, and replaced it with the remainder of her Nembutal-laced drink. Now there’d be nothing but her fingerprints on the lethal glass. The two glasses of wine he’d poured for them went into his tote bag for disposal with her phone, as did the job offer letter. Next he wiped down the wine bottle and the vial of Nembutal, using chlorine bleach to remove his DNA.

He stopped and looked at her body, slumped against the side of the couch. Clenching his jaw, he forced himself to pick up her hand and press her dead fingers onto the wine bottle and Nembutal vial. Another wave of nausea hit him but he choked it down. Done. He left the bottle and vial on the coffee table in front of her body.

Then he went over to her computer. He’d composed her suicide note earlier that evening and now he typed it into a new Word document, keeping his gloves on.

I’ve betrayed all my values and can no longer live with what I’ve done. Pam Weller forced me to fake the experiments with her. She said she would destroy my career if I didn’t do it. I didn’t think I had a choice but now I know I should have refused. The two of us made the whole thing up. I’m so sorry, I just need to end it. Forgive me please.

He left the suicide note open on her computer desktop and reviewed the scene again. Sure, his DNA would be in other places in the apartment, but it was unlikely that a full-scale CSI-type investigation would happen in the case of a suicide. And even if it did, they’d just find the DNA of an unknown male. No big deal for her to have had a visitor, he probably wouldn’t be the only one. He wasn’t in any DNA database, so there was no way they could match it to him anyway.

He took a last look around before he left. Then he walked home to his condo through the cold December night, pausing on the BU bridge to burn the offer letter and dump the incriminating contents of his tote bag into the Charles River. His head pounded as he leaned over the side of the bridge, watching her phone fade from sight and splash into the water. He’d killed her. A woman he’d had sex with, now cold and dead. Enough. He pushed back from the railing and forced himself to stand up straight. It had to be done.

He silently thanked Holly for her unknowing sacrifice. At least she’d be pleased by Pam’s coming destruction.