CBS | 9:00 pm

Darius (Santiago Cabrera) has to dig deep to demonstrate his loyalty to Grace and Harris (Jennifer Finnigan, Ian Anthony Dale) in "The Human Strain," the first of two new back-to-back episodes. Liam (Charlie Rowe) helps Jillian (Jacqueline Byers) settle into her new job. Then, in "Keeping the Faith," Darius has to revisit a difficult part of his past in seeking a friend’s killer. Also, Liam learns who’s been in cahoots with the Russians.