DS9 S4E01 - The Way of the Warrior

Sisko is surprised to find a Klingon armada uncloaking around the station. Their purpose is unclear, so Sisko calls in eveyone's favorite Klingon expert, Worf. At loose ends since the sad loss of the Enterprise-D, Worf doesn't know if he will even remain in Starfleet. Until then, though, it is his task to discover what he can about the Klingons' purpose. The answer has the potential to reshape the entire Alpha Quadrant.