The hit sci-fi series Silo is back today for a third season, streaming exclusively on Apple TV. Based on the book series by Hugh Howey, the acclaimed series sees the human population living in a vast underground bunker, but no one really knows how it came to be.

In the third season, a split timeline narrative begins to reveal some of the show’s biggest mysteries. In the present timeline, Juliette (star Rebecca Ferguson) struggles with amnesia, while in the past timeline, flashbacks show who, how and why the silos were built in the first place.

The main character Juliette escaped the main silo in season 2 and found out a lot of provocative information, and season 3 starts with her return. But, frustratingly, she can’t immediately spill the beans as she is facing a rather inconvenient spate of memory loss.

Meanwhile, the flashbacks fill out the history of the world. The jump into this part of the story was teased in the final minutes of the season 2 finale.

The depiction of the past also helps mix up the show’s formula, escaping the usual settings of the underground bunkers into a lush world of alt-history Earth with unstable geopolitics motivating the creation of the silos, seemingly under threat of nuclear war.

Critical reviews for season three are looking solid, with Silo boasting a 100% Rotten Tomatoes score right now. Many reviews indicate that the culmination of events in S3E9 and S3E10 make for the show’s strongest season finale yet.

Apple has already renewed Silo for a fourth and final season, which will probably premiere next year. Unlike many modern mystery box shows which go and forever and get cancelled without resolution, Silo is on a path to a conclusive end, and season 3 makes moves in that direction.

If you haven’t seen the show before, you can catch up now with all episodes streaming exclusively on the Apple TV app, with an Apple TV subscription. You can get a seven-day free trial for new accounts here. Watch on all manner of devices, including smart TVs, games console, Android, and even on the web at tv.apple.com.