Okay, I put the clock in the plant. I gather I'm suposed to snoop around the front where Xavier is but Gabriel won't go into the front. He walks back into the place with the fireplace and sofa but when I click on the door, he sits down, looks at Xavier walking in and gives a sneaky kind of smile. I click on the door as soon as he walks into the room but he always just sits down.

Seems like the pointer is wrongfully clicking the chairs instead of the door, where you're actually pointing it. Try to click the chairs instead, or even the bar. Might be worth a try.
Or you have to go back to another savingpoint. Because you have been saving in different saves, right? ;)

(stuff you learned from playing games in the 80's and 90's; save often, and on different slots.)