He was sent into JFK from Rome, arriving he quickly murdered a taxi driver and stole his car, which he used it to get to Portland. There he began stalking Nick, searching for his key, watching him as he went to multiple locations following a case he was on.
In the next episode, David follows Nick into a bar, where he is meeting a friend of his Bud. Nick senses he's there, but David moves so Nick doesn't spot them. He then breaks into Nick and Julliet's house, and starts going through it trying to find the key, upon finding nothing, he leaves the house, and Juliet who he left unaware he was there alone.
A while later, while Nick was studing his ancestors texts in the trailer, David some how finds it. As Nick was leaving he snuck upon Nick, however Nick spotted him in the window, and dodged at the right moment. The two proceed to fight, David being unnaturally strong, but Nick being just as powerful. Nick managed to knock the Nuckelavee to the ground and held him at gun point, but David rolled under the trailer escaping, Nick ran round, but David tricked him and doubled back. Entering the trailer, the two continued to fight, David knocked Nick down, but grabbing his leg, Nick twisted it knocking him to the floor. Nick then ran to the weapons cabinet and grabbed a maul (a giant war hammer). David charged into him trying to cause him to drop the hammer, but Nick pushed him off, and killed the mercenary by repeatedly smashing him with the hammer. Upon investigating the body, Nick found he was after his key, and thus later dumped his body in a river.