You're being pursued by Alex, so escape your strange office.
Alex will call you and try to locate you by the sound of your ringing phone. In this world there is no way to silence or turn one's phone off.
And because of that, you can call Alex as well, to try and locate him in a similar manner.
Also, try knocking on some doors. Maybe you'll hear the answers to your questions from the other side.
Tab - Get phone out / Put phone away
Q - Call / Answer phone
E - Hang up / Ignore call
Left Click - Interact / Knock on door
Esc - Pause menu from which you can view the controls, exit the game or change the options
Update, April 28, 2017:
Weird this is still being played a lot. Didn't expect anyone to play it outside of the little jam I made it for. Thanks.
For anyone interested, I'm making Nighttime Visitor anew.
Nighttime Visitor was made in a few weeks. I like the idea, it seems others do too, but it's far from being something really good. So I'm taking the premise and spending a lot of time to make something new with it. I wouldn't exactly call the new game a "remake", I think it would fall into "reimagining" territory. You could consider this game a proof-of-concept for the new game, or something. Anyway, follow development of it at my blog here:
Update, June 10:
After a long time, I've fixed a few more miscellaneous problems. Alex's AI has also been improved and altered a bit, and I've finally optimized the game a lot. It should run way smoother for those who experienced lag, and at the same time also look slightly better.
Update, Nov 4:
I fixed a few little miscellaneous problems, and one big one concerning Alex's AI. Unluckily, I had never noticed this myself until I saw other people play and experience it. Logically, the code worked correctly most of the time, however I didn't take into account the order it was executed, and under particular circumstances Alex wouldn't work correctly. But now he should be a bit more competent and consistent after I've made the fix. For that, the game will probably be harder too.
Performance has also been improved a bit, hopefully.