'Breaking Bad' recap: End Times
Then, Jesse's world comes crashing down around him when Andrea calls from the hospital -- Brock is sick. They don't know what it is, but it started out like the flu. While we all feel that pit in our stomach, Jesse doesn't catch on until he goes out to smoke and notices his ricin dose is missing. Just ... the worst thing ever.
After telling Andrea to tell the doctors it's ricin, Jesse goes to see Walt. While Walt mopes around about his impending doom, Jesse picks up his gun, points it at Walt, and accuses him of poisoning Brock. It doesn't make sense -- Occam's razor says Brock snuck a cig from Jesse's pack and ended up poisoning himself -- but what follows is a paranoia-fueled showdown where Walt ultimately decides that Gus must've poisoned Brock, in order to get Jesse to come kill him. They decide to take care of Gus together.