He is hunted down by Danny Brickwell and Michael Amar because he is the only one who can disable the nukes that Darhk has launched, forcing Team Arrow to rescue him and recruit his assistance in disabling the nuclear missiles, although his best efforts are only able to stop the missiles after one missile is launched and redirect that missile to a relatively small town. Before teaming up with her father to stop the missiles, Donna revealed to Felicity that Noah didn't abandon them; rather, Donna and Felicity left Noah after Donna discovered his life of crime, not wanting their daughter to be corrupted.
Donna
Felicity