The $30 million condo unit high atop East 57th Street sits empty, stripped of its furniture and possibly abandoned. The mortgage on the 72nd floor residence at 432 Park Avenue is in default, its guarantor appears to be in custody in China and the unit owner’s identity is uncertain.

Now the firm that owns the debt wants to seize the 4,000-square-foot property on Billionaires’ Row, where high-end real estate purchases are often shrouded behind layers of LLCs.

In a lawsuit filed last week, Maverick Real Estate Partners is seeking to foreclose on the three-bedroom unit, hoping to sell it “on an expedited basis on the grounds that the property is vacant and/or abandoned.”

Maverick alleges the owner of unit 72A — listed as an offshore LLC — has failed to make mortgage payments since March, throwing the loan into default.

In May, Maverick bought the $13.75 million mortgage from China Citic Bank, property records show. Just over $1 million of the principal loan has been repaid, according to the lawsuit. But exactly who borrowed the money remains something of a mystery — as has been the case with other high-end condo purchases on Billionaires’ Row and around Manhattan.

The entity that controls unit 72A is registered to an Upper East Side unit at 200 East 65th Street, according to court filings. That unit is in turn controlled by Eagle Harvest LLC, city property tax records reveal. The identity of individuals behind that company could not immediately be learned.

An attorney for Maverick declined to comment on the case.