Breaking Bad Season 4 Episode 13 (10/09/11)
Walter White won on the season finale of Breaking Bad.
He came up with a plan that led to Gus' death and it came to mind after Jesse told Saul about Gus visiting Hector. Walt then did so himself and convinced the old man to play a role in his revenge scheme.
Hector visited the DEA, didn't tell them anything, but was spotted by Tyrus. When this information was relayed back to Gus, he determined that he had to kill Hector. So he arrived at the retirement home and was about to inject Hector with something... when Hector rang his bell and the explosive Walt had hooked up went off, killing him, Gus and Tyrus.
Walt met with Jesse on the roof of a parking to garage to discuss the development, after the pair blew up the super lab. Jesse said Brock was poisoned with Lily of the Valley, a type of flower, not Ricin after all. So Gus was not behind it, but of course he still had to go, Walt said. Jesse then drove away, Walt called Skyler and said they were safe and the episode ended with a close-up of a flower pot in Walt's backyard.
It was Lily of the Valley.