It started as documentation. That was the honest answer, if he ever had to give one — which he wouldn't, because the only person who knew about the notebook was him, and he intended to keep it that way until he died or transferred universities, whichever came first.

Week one he'd written it down because he was frustrated, and frustrated people needed outlets that weren't screaming in a sterile environment. Week two because the pattern was interesting. Week three because he was starting to suspect something, and suspicion without evidence was just anxiety with better posture, and he refused to operate on anxiety.

Six weeks later he had three pages of timestamped entries and a conclusion he didn't love.

The first entries were damning. Objectively.

Monday. Knocked over buffer solution reaching for pipette. Contaminated sample B. Wednesday. Dropped tube rack. Caught it. Still rattled everything. Friday. Pipetted wrong volume. Caught it herself before running gel. Didn't tell me until after.

Classic clumsiness. Spatial carelessness. The stuff Riley had warned him about. Keep an eye on her, that tone that meant she's brilliant and also a liability and you're the most responsible person I have. Theo had taken the assignment seriously. Of course he had.

That held up for exactly three weeks.

A Tuesday, week three. She'd walked in not knowing he was already there, and spent forty minutes running a serial dilution with the kind of quiet unhurried precision that made him stop what he was doing and watch. Not glance. Watch. No spills. No miscounts. Steady hands. She caught a contamination risk before it materialized, rerouted without commentary, kept moving. Like someone who knew exactly what she was doing and didn't need an audience for it.

He'd written: Dilution series. Flawless. No incidents.

And then, because he was thorough: She didn't know I was here.

He'd stared at that second line longer than the data warranted. Started looking differently after that.

The pattern, once he was actually examining it, was uncomfortably legible. Incidents didn't cluster randomly. They clustered around him. Around proximity to him, specifically. She dropped things when he leaned over to check her work. Pipetted wrong volumes on mornings they'd argued methodology before starting. He'd filed the day-one contamination under carelessness. He was revising that filing.

He cross-referenced. Days Riley stayed late: her error rate, unremarkable. Days Marcus borrowed equipment and hovered: unremarkable. Days it was just the two of them: the numbers went sideways with a consistency that would've been impressive if it weren't inconvenient.

She wasn't clumsy. She was nervous. Specifically, around him.

The question was why.

He ran possibilities the way he ran everything. Without attachment. Option one: professional intimidation. His reputation wasn't warm, he knew that. The guy who showed up before anyone else, corrected people quietly and without apology, had been on a PhD-track project before most people his age had picked a thesis topic. Plausible. Option two: something adjacent to professional intimidation but meaningfully different. A distinction he kept not examining, because examining it required him to sit with what it implied. That he'd noticed her mouth before he'd finished reading her file. That he knew exactly how she held her breath at the microscope. Option three: coincidence, and this whole exercise was what happened when you gave a perfectionist a blank notebook.

He looked at the three pages.

He wasn't wrong about the pattern.

He closed the notebook. Opened it again.

She works better when I'm not watching.

The implication sat there, patient, waiting for him to stop pretending he hadn't already understood it.

So stop watching.

He closed the notebook.

He already knew he wasn't going to.