Summer's over, which means deal season is here in New York City, and Silverstein Properties started it with a bang.

Law firm Kelley Drye & Warren LLP has signed a 15-year, 103K SF office lease at 3 World Trade Center, the skyscraper Silverstein opened last year and is working to fill up. The 183-year-old law firm plans to move its offices from 101 Park Ave. next year, Silverstein announced Wednesday.

Kelley Drye will occupy three of the 1,000-foot-tall building's 80 floors, and it will be the first law firm inside the building. It joins anchor tenant GroupM, as well as McKinsey & Co., IEX, Casper, Better.com and Hudson River Trading in the tower, which opened at 40% occupied. A Silverstein spokesperson said the building is now 56% leased.

“As our firm looks to the future, we wanted office space that mirrors our commitment to innovation and growth,” Kelley Drye Chairman Jim Carr said in a statement. “3 WTC is a state-of-the art building that will allow us to serve our clients in a transformational new space and provide a quality work environment for our employees."

Silverstein's Jeremy Moss and CBRE's leasing team led by Mary Ann Tighe and Ken Meyerson represented the owner in the deal, while Transwestern's Patrick Heeg and Ryan McKinney represented Kelley Drye.

While leasing has consistently moved along for 3 WTC's offices, the same can't be said for the building's large retail footprint on the ground floor, which is managed by Westfield. Two restaurant groups pulled out of deals for the building last year and most of the 75K SF of retail in the tower "remains embarrassingly empty," according to the New York Post.

While Silverstein continues its work in filling up 3 WTC — and keeps looking for an anchor tenant to kick off its last building on the site, 2 World Trade Center — it is also planning on bidding on one of the only parcels in the vicinity it doesn't control: 5 World Trade Center.

Gov. Andrew Cuomo launched a bidding process for that site, which could support an up-to-900-foot building, in June. Silverstein has been in talks with Brookfield to bid on that site, controlled by the state, Commercial Observer reports. Bids for 5 WTC, which could also attract One World Trade Center developer the Durst Organization, Vornado, Tishman Speyer and others, are due Sept. 20.

UPDATE, SEPT. 5, 12:15 P.M. ET: This story has been updated with 3 WTC's current occupancy.