Gus Fring is dead - nursing-home explosion with Hector Salamanca.
Walt engineered Gus's death after a long war for the meth empire.
Hank is alive and recovering; he does not know Walt is Heisenberg.
Season 4 ended with Walt using Hector as bait and bomb. Before that, Walt poisoned Brock (lily of the valley, not ricin) to turn Jesse against Gus.
Hank's Fring investigation produced real institutional heat that does not vanish with Gus's death.
Walt partners with Jesse; early cooks and Tuco danger establish the trade.
Skyler grows suspicious; Hank is DEA family.
Walt's Heisenberg identity begins.
Tuco falls; distribution expands; plane crash aftermath hangs over ABQ.
Jane dies; Jesse breaks; Walt's moral freefall accelerates.
Saul Goodman enters as counsel.
Gus Fring institutionalizes Walt and Jesse in the superlab.
Gale is killed; Jesse pulls the trigger under coercion chain.
Hank survives the cousins; becomes obsessed with Heisenberg evidence later.
War with Gus ends in Gus's death via Hector's bomb.
Walt poisons Brock to turn Jesse; lily of the valley, not ricin.
Hank still does not know Walt is Heisenberg.
Season bridge: everything above is end of Season 4. S05E01 ("Live Free or Die") has not started.
Cutoff discipline: every fact above ends at S04E13. Do not import anything from S05E01 ("Live Free or Die") or later.