Sorry Marky, I was a bit rushed sorting the dinner out. Anyway, here you are . . .

Warning Spoiler

• The silver key is behind the boom box. Look down the room ("your" back to the dart board) and you'll see a sneaky little protuberance.
  
  
• As far as it goes, my thinking re. the exit code was correct. What I wasn't aware of, until I looked at the book under the UV light (that's what I missed before), is that Open Triangle with the apex pointing up is a diffent value to Open Triangle with the apex pointing down. As Bob says, the exit code is 718; though overall not a bad performance after a night shift.