I've been working my way through Chapter III. I've got to the part in The Source where Dandelion is supposed to lead me to the house in which Alvin is being held by his kidnappers. When I get there and go inside, it's empty. From looking at some walkthroughs, it seems that there are supposed to be people in there - Alvin and some assassins. Dandelion now refuses to talk to me further, and I can see no way to progress the quest any further.

Has anyone else had the same problem? Does anyone know of any solutions which don't involve reloading a much earlier save? (I've already reloaded several slightly earlier ones, but I ran into the same problem. I'd rather not load any earlier than that, as I've made several hours of progress since then)