Arman reluctantly embarks on a submarine research trip sponsored by his father; at the Incirlik Air Base, Hatice reports an unusual radiometer reading.

Amid a search for survivors in Kos, Arman and Defne rush to find Kenan before sunrise; Felix and Cem scramble to restore electric power to the town.

Inside the submarine, tensions come to a head between Arman and Umut; when Baris' actions unravel, Erenay confronts an impossible dilemma.

Arman and Yonca must swim out to fix a rupture, but the submarine is still in jeopardy; the Yakamoz crew discovers an intruder.

After Hatice reveals a shocking truth about Erenay, Umut and Yonca begin to suspect Defne; the crew tracks an airplane; Cem makes a devastating choice.