Security and one of our two night housekeepers meet me on 3 by the elevators, asking if I'd noticed the smoke and if I had any clue where it was coming from. Yes and no, in that order. We've had smouldering cigarettes tossed into the planters lining the atrium before, so we split up and check all those and nothing. Smell's a little stronger by then and it seems a little more hazy, so I get the front desk to call the fire department.
A couple of policemen heard the call and pull up while we're waiting, they mention the smoke smell the second they walk into the lobby so they start looking too. The haze isn't getting any worse, but it still smells like wood or paper burning. A couple of minutes later two fire trucks pull up, maybe a dozen guys total, and everybody's trying to find where this smell's coming from. Fire crew thinks it might be electrical, a ballast in a fluorescent fixture maybe, so we call the head engineer to ask where the breakers are. He doesn't answer, but we manage to get his assistant on the phone and let him talk to the fire chief. They go back and forth for awhile, the chief finally tells the engineer he needs to come in and start going over everything since there are about a dozen breaker panels and we have no clue which goes to what - and still can't find where it started.
About 3:45am the fire dept admits they can't find anything, visually or with heat sticks, the smoke's dissipated and the smell's clearing out so they pack up and leave. The engineer got here a few minutes after that and has been checking stuff system by system ever since and still no clue what happened for sure. He suspects a fan motor in the restaurant's heating system burnt out, the smell was strongest up in the restaurant ceiling, but it's going to take a lot longer effort yet (once day shift comes in) to track it down for sure.
When I started doing Night Manager shifts, Knight said the biggest part of the job was knowing when to yell for help and who to wake up.
ETA: I drew a card from the Halloween Tarot before I came in tonight, the Hierophant (Mummy) reversed. Any thoughts on how that would tie into this?