Eph (Corey Stoll) makes the toughest decision of his life in the upcoming episode of FX's horror drama series "The Strain."

In "Fallen Light," TV Guide reports that Eph will have to pick on whose life he will save, Zach's (Max Charles) or those of the citizens of New York. It appears that the scientist will only get to choose one between the two options, and it is certainly destroying him. On one side of the spectrum is his son, whom he loves, while on the other, an entire population, whom he swears to protect. Who will Eph choose?

Meanwhile, his relationship with Nora (Mia Maestro) will reportedly come at a crossroad. Who is she rooting for? Will she convince Eph to give up his son, whom she has come to love as well, for the greater good? Or will she tell him to follow his heart as a father, and forget the rest of the world?

Last episode, Eph, Nora and Fet (Kevin Durand) saved Dutch (Ruta Gedmintas) from Eichhorst's (Richard Sammel) clutches. Viewers also saw the monster's past when he was still a Nazi soldier. Apparently, he was once attracted to a woman named Helga (Julie Engelbrecht), but he got her killed after denying his relationship with her.

Dutch apparently reminded him of Helga and that was why he was playing with her. The rest managed to save Dutch before Eichhorst made a meal out of her, injuring him with a silver grenade. The vampire, however, still escaped and who knows when he will attack once again.

As for Abraham (David Bradley), he did find the Occido Lumen, but was knocked out by an unknown assailant immediately after taking a glimpse of the tome. The man who accosted him turned out to be Rudyard Fonescu (David Schall), the boy he saved from Strigoi in Austria in 1966. Abraham decided to bargain with Rudyard, but he ended up giving the latter the idea of selling the book to the highest bidder.

"The Strain" airs Sundays at 10 p.m. EST on FX.