SPOILER ALERT: This story includes details about the Season 2 premiere of NBC’s This Is Us.

A steady hour of trending Twitter activity hit the stratosphere at the end of tonight’s Season 2 premiere of NBC’s juggernaut drama This Is Us. The episode culminated in the revelation of a burned-out house, presumably (but not conclusively) pointing to what killed Jack Pearson, the central character played by Milo Ventimiglia.

Immediately before the final image of the scorched house, Jack confesses his alcoholism to his wife, Rebecca (Mandy Moore). “I have a problem, Rebecca, and I have hidden it from you for a very long time,” he says. “I need to get a handle on it before I can walk back into that house. I’m sorry, baby, but I need to fix this on my own.”

While she reassures him that they will face the problem together, as husband and wife, a mournful cover of U2’s “One” playing underneath the scene foreshadows what’s to come. As the scene dissolves to the children crying, Rebecca pulls up outside and realizes what has taken her husband and the father of her children.

Until the climax, the episode had simmered along at a more moderate temperature. During an opening montage re-establishing the central multi-timeline story, William (Ron Cephas Jones) reads from a book of poems written for his biological son, Randall (Sterling K. Brown, fresh of his Emmy win). In one sequence that NBC released over the summer as a promo clip, Rebecca confesses to Randall that she had to be talked into adopting him. “Your father wasn’t perfect,” she allows. But “he pushed a stranger on me, and that stranger became my child, and that child became my life. He became you.”

As cast members and showrunner Dan Fogelman discussed during Deadline’s pre-Emmy panel on the Paramount lot last month, Season 2 picks up the day after a wrenching split between Jack and Rebecca. The hour found the children trying to make sense of their parents’ separation; in the present-day storyline, Jack is notably absent and the episode builds toward the explanation for why. It had long been expected that there would be a major revelation about Jack’s death, and jaws were reportedly dropping on set as cast members got their first look at the script for the premiere episode. “The first episode has a big, giant piece of the puzzle,” Dan Fogelman said during TCA press tour in August. Ventimiglia told Deadline the sense of expectation was almost overwhelming, “like we’re all carrying this one big secret.”

For NBC and all of broadcast TV, This Is Us has been a rare ray of hope breaking through the storm clouds. By any measure, the show has been a generational hit. It notched several milestones during its debut season–earning NBC’s first scripted series total-viewers weekly ratings win in 13 years, helping the network claim another season demo crown and earning 10 Emmy nominations, including one for best drama.

After tonight’s shocker, the resulting explosion of buzz is serving as ample explanation for the network’s swift and unusually forward-looking two-season renewal of the show just three months into its run.