While Phoenix and Dominé attend the party, Cal breaks into the nearby bank and convinces the guard manning the security systems that he's from the security company himself, and gets the guard to scan through recent security footage to see if anyone has broken into the building. He doesn't find any information about a break-in (other than his own), but he notices gaps in the building's security that would allow someone to get to the roof without being noticed, so he heads to the roof himself.
A police drone begins patrolling the neighborhood from above, so Eden gets off the roof and mingles with street traffic outside of the apartment, where he sees the drone come crashing down, either hit by an EMP attack or hacked. He decides to get to the apartment roof, and talks his way past security and onto the elevators. From the floor below the penthouse, he finds a stairwell to the penthouse roof, and fries the electronic lock to get out onto the roof itself.
At the party, Phoenix is introduced to Sev Derstine, and later to a man named Terry, who happens to be the "husband" of Nellie Razen, the sniper who Cal and Eden think is still in the area.
On the bank rooftop, Cal doesn't find anyone, and so waits on the rooftop looking for trouble at the party. He sees Eden emerge on the rooftop, but is almost surprised by Nellie as she crosses the roof to attack him. She fires at him a couple of times, but he gets to the safety of the stair tower and contacts the police and then Eden. She blocks the doors somehow so that he can't get out easily.
Terry tries to stab Phoenix with some kind of hypodermic needle, but she manages to notice and moves away through the crowd, just as Nellie starts firing at her from across the street, hitting someone else in the crowd accidentally. Phoenix dashes through the crowd towards the interior of the penthouse while Eden fires back at Nellie, trying to keep her pinned down. Although partly successful, Nellie manages to fire into the (mostly glass) penthouse and Phoenix takes a couple of injuries, one minor and one very dangerous. She manages to make it into the foyer where many people are trying to crowd the elevator, so she finds the stairs instead, but as she is just entering the stair tower, Terry surprises her and kicks her down the stairs, where she passes out to the sound of police feet running past her into the penthouse above.
On the bank roof, Cal burns through the door hinges with his pistol, and engages Nellie with his taser. He exchanges a couple of shots with her and gets her out into the open where Eden can hit her from across the street. She's pretty badly injured but still alive when police pour out of the bank stair tower and open fire at her.