Swamped

You think back to what you learned from working here. You weren't a doctor, but sometimes you had to be informed of sensitive matters in order to properly update the records. And sometimes, when you were being briefed, patients would wander nearby. So another member of the staff would start tapping the walls nearby in a particular pattern to inform you if they saw a patient approaching. Then you'd change the subject until you got another pattern indicating they were out of earshot.

This is the night doctor, so you aren't sure if he'd know the same code they used during the day. But it's your best shot. You grab a nearby tree branch and tap it lightly, but deliberately, against the window. It should be clear enough that it's coming from the window, so someone who doesn't know the pattern will look there first. You do position yourself to get a look in without being spotted in return, though.

The doctor glances around, confused for a moment, then he spots the intruder. He quickly shuts his eyes.

But the intruder has turned their attention directly to the office door. As if they were instinctively looking for a patient to be coming from that direction. It takes them a few moments before they turn to the window.

So. Somebody who worked in the hospital? Or perhaps still does?

You can't do much except watch as the intruder rifles through a few boxes, grabs a piece of paper, and then leaves the room. You wait a minute or so and then tap out the all-clear.

The doctor comes over to the window. You wonder if you should go with the original plan and let Mortimer greet him, or just do it yourself.

Either way, you've just realized that he's likely to want an explanation as to how whoever it is knows the hospital's secret alert codes.