I already did this, there is a save a nd i dont have any option to visit grandpa house even i have mask at the bag.If you bought the mask (how the game suggest you should have the option to go to your grandpa's house when you click the bed.
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This is from a new game I just started where all I did was go to ralph to the house the first time to explore, go to the police to get the key and nightvision goggles and then buy a mask at the mall.