“Doctor Who” is all about the two-part stories in Season 9. Viewers were left with a massive cliffhanger in episode 3. The Doctor (Peter Capaldi) and Clara (Jenna Coleman) went to an underwater base where they seemed to meet ghosts. The two were separated, but the Doctor decided to hop in the TARDIS and go to the past to find out how these undead creatures could exist. After he left, Clara saw the Doctor as a ghost in the water. According to the episode 4 synopsis, it'll be hard to change the Doctor's fate.

In the episode, aptly titled “Before the Flood,” the Doctor will visit the underwater base before it's filled with water. “On a remote Army outpost, a fearsome alien warlord -- the Fisher King -- sets in motion a twisted plan to ensure his own survival,” the synopsis teases. Of course, this plan will affect not only those around him, but everyone throughout the universe.

“Is this chain of events inevitable?” the synopsis asks. “And can the Doctor do the unthinkable?” The Doctor has plenty of rules about not changing fixed events in history. He is hoping that by going to the past, he can travel back to the future and fix the ghost problem. However, he might not be able to stop the ghosts without interfering with history. Rules were made to be broken, right? Yet the Doctor doesn’t seem to be in a rebellious mood in the promo video.

In the trailer, the Doctor tries to accept that his death is near. “This isn’t about saving me,” the Doctor says. “I’m a dead man walking.” The Doctor might not want to stop his own death, but the Time Lord has never been able to stop himself from saving others. 

Watch the promo video for “Doctor Who” Season 9, episode 4 below:

The Doctor might not have to “do the unthinkable” if Clara somehow steps in. The companion is not mentioned in the synopsis, but it seems unlikely that she would just wait for the Doctor to return with a solution while lives are in danger, especially after seeing him as a ghost.

“Doctor Who” Season 9, episode 4, titled “Before the Flood,” airs Saturday at 9 p.m. EDT on BBC America.