A mouse in the house [update, 9 Oct]

No - there's no metaphor here.
There's just a mouse in the house.
I've not seen the mouse, but I infer its existence from actions of the dog & one of the cats - sort of like Neptune was discoverd by folks noting pertubations in the orbit of Uranus.

In the best of all possible worlds the mouse will show itself, perhaps allowing 'catch and release'.

In a less perfect world, it will die behind or under a heavy piece of furniture, its corpse disclosed only when it decays - imbuing the surroundings with a truly horrid death-smell.
(Yes, I speak from experience!)

Time, alone, will tell.

Update, 9 Oct: the carcass was left on the threshold of our bedroom door. Our 'mouser' is a bit confused: he brings mice INTO the house, presumably to demonstrate his hunting skill. This was a far better outcome than some!