I've Googled this from here to the ends of the earth and haven't found a solution. I've seen other people with the same problem but the best response they've gotten is to just not do this quest.

The quest is the Secret Garden quest in France. Gaston Dutiel is hearing strange noises and wants your sim to investigate. Hey, sure thing, except he's never home so I can never get into the basement and into the tomb! I've already quit and come back to this several times, even had my sim camp out in front of his house for a full 3 days waiting for him to come home.

Is there some cheat I'm missing that would force him to come home? Is there some way to break in? Someone must have had this issue and found a way around it.

Well if you just need to get into the house you could go to edit town and add another sim to the Dutiel household.

But first you could just try resetting Gaston, he could just be stuck somewhere.

He seems to live at the nectary. I don't know if this is normal or not.

Of course ten minutes after posting this I thought of giving him a mail order bride. Who is not seeing someone else. The scandal.

Thanks for replying! If nothing else this'll bee google-able when someone else runs into this issue.

It's always quite annoying when the game decides to make those Sims merchants in a vacation land that live above a quest tomb (can happen in Egypt, too). But in your case I really wonder where Gaston's family is. Because in a "fresh" France the Dutiels are a family of three - Gaston, his wife Lea and their son Remy. Try to locate these first, perhaps, because as far as I remember, whenever I did that quest I had to deal with both Gaston and his wife during the whole sequence. Another solution might be to use a mod like AwesomeMod or MasterController in order to make Gaston Dutiel active for a few minutes. He will quit his job at the Nectary immediately and chances are that then he will be replaced by another French Sim and return to his house.