A $40 million compound with its own little harbor could re-write the record books as the most expensive listing ever sold in the Florida Keys. 

The staggering complex on Plantation Key hit the market last week and includes an 8,200-square-foot main house and a 1,500-square-foot guest house — or caretaker’s cottage — set against the blue greens of the Atlantic Ocean. 

Todd Maino, a builder and sports fisherman, owns the property with his ex-wife, Catherine McMullen. McMullen is the daughter of the late John McMullen, who brought National Hockey League play to the Garden State through his ownership of the New Jersey Devils. 

Maino and Catherine McMullen paid $5 million in 2018 for the 7-acre property, property records show. Plantation Key is one of the 45 inhabited islands that make up an archipelago stretching 220 miles from below Miami southward to Key West. 

The land Maino and McMullen bought had five houses on it at the time, with most used as research labs by naturalist and horticulturalist Herbert Zim who, with his family, owned the property for more than 70 years.

Zim’s fawning over the flora still shows the benefits of his touch, Maino said. “You look around and it keeps with what he was about.”

Maino believes he, too, has put a lasting aesthetic imprint on the property. The New Jersey native traded a career building Starbucks and 7-11s in the Garden State for the pull of “a rare and peaceful place” that he conceptualized as a builder and someone who has lived in the Keys.

Any prospective purchaser may find Maino to be a street-smart negotiator, though. He grew up in the Sopranos’ stomping grounds and owned the slice shop, Pizza Land, that the show featured. 

The result of Maino’s conceptualization is the main house with five bedrooms, six full bathrooms and two half baths. White diamond marble and teak floors run throughout, while tall glass windows look out over the Atlantic from every room — except one. 

An elevator paneled with white shaker wood and whose floor is a mosaic nautical compass goes to the second floor. A large vapor fireplace that uses ultrasonic technology and LED lights to create virtual three-dimensional flames is nearby.

Beyond the main house is a 3-acre area with the recently-renovated 1,500-square-foot house that, according to the property’s listing, can be used by “guests or a caretaker.”     

For those who want to expand, there is enough buildable land near the guest house to develop another two houses, Maino said. 

The property’s outside attributes are designed to be just as, if not more, engaging than the homes. A 120-foot infinity pool containing 90,000 gallons of water sits in front of the main house. Beyond the pool lays beach front that runs 480 feet, more than the length of a football field, and backed by a large expanse of beach. 

Maino is listing the property as a total package but is open to splitting the sites for a total of $42 million: the 3 acres with the main house and pool for $27 million, and the other 4 acres containing the cottage and building rights for $15 million. 

The Plantation Key property has a lot of wiggle room to become the Keys’ most expensive listed home sale. Barstool Sports president Dave Portnoy set the bar last year with his $27.75 purchase of a compound in Islamorada, down the road from Plantation Key.

Maino also has close-quarters competition from a property for $42 million that sits a few doors down from his complex. That site listed over a year ago with no takers. 

There are “definitely challenges” to selling strata-priced homes in the Florida Keys, said listing agent Angel Nicolas of the Nicolas Group at Serhant.  

“The market narrows to technically the 1% of the world,” Nicolas said. “But are there people interested in the area? Yes, 100%.”

The listing adds another multimillion-dollar property to the Florida Keys, appealing to buyers who want their beauty, and, in growing cases, its presence as a lower-cost alternative to the eight-figure estates just north, in the Miami and Key Biscayne areas. The attention is a far cry from the Keys’ raw and ramshackle beginnings as a mangrove-clotted cluster of islands so brutal that ravenous mosquitoes and fleas could leave a dog outside at night dead before morning. Conditions dramatically changed in 1912, when Standard Oil cofounder Henry Flagler completed his rail line connecting the Keys to the mainland, opening the islands to prospective residents and commerce.

Back on Plantation Key, it’s just Maino and his Belgian Malinois, Legend, knocking about the place. Legend appears just fine with the arrangement. “He thinks he’s in a giant tropical dog park with great sunsets,” Mr. Maino said.