I'd use the second house ruler to represent your key, and your significator would be the first house ruler. I saw mars, which represents your key, in your enemy's house. but mars is about to trine your significator, so I think you'll find your key. I don't know how to read where it is though.
Pluto is the modern ruler of your 2nd house. I think it is best to follow paths of both traditional and modern rulers to see where they lead.
Pluto is in the 4th house - "If the ruler of the 2nd house is in the 4th, then the thing is in that part of the house where the oldest person in the house sleeps or spends a lot of time or in the middle of the house, or in the most ancient part of the house, where either her Father or older man sleeps or spends a lot of time."
Pluto is in Capricorn - "If the significator is in earth signs, then the thing is hidden on the ground or earth, under or near some pavement or floor; If you find the thing to be mislaid out of the house in any ground, it notes near a Bridge or Stile where people come into the ground."
"The sign on the cusp of the 4th house and its ruler help to describe the locality of the item and in particular the quality of ground it lies upon."
"Angular houses - the significator for the missing item angular shows that it is near its owner, and suggests a quick recovery. "
"The significator of the property in a moveable sign generally shows that it is not far from its owner."
Now for Mars...
Mars is in the 7th house - "If the ruler of the 2nd house is in any angle (Houses 1st, 4th, 7th or 10th), then the thing is within the house of the Querent."
"If the ruler of the 2nd house is in the 7th, then the thing is in that part of the house where her partner or servants have most to do."
"If the significator is in fire Signs, then the thing is near the chimney, or where Iron is, or in or near the walls of the house."
Tandy, I had just turned in a car (end of the lease) so I took the car key off the ring and it became a stand alone key. I can't recall if I went to a family member's home although since I turned the car in, I did visit my family in another state for Thanksgiving. Knowing me though, it's in or close to the house.. Glad your mercury is in effect!
If the absence of key is causing financial obligation - look at 2nd house and 8th house. 2nd house would show responsibility for property and 8th house would show what you owe for non responsibility. Mars in 8th! aspects to 11th house moon venus - at an older female friends house or near a 12th house place of hers?