DS9 Season 4 Episode 12 Paradise Lost

Plot

Earth has been placed under martial law due to a seemingly imminent Dominion invasion, but Sisko believes that there is more going on than meets the eye. With the aid of Deep Space Nine's security officer Odo, and Cadet Nog's connections with an elite and selective group of cadets at Starfleet Academy, Sisko gathers evidence that Admiral Leyton is planning a coup d'état. He takes the information to the Federation's president, Jaresh-Inyo; however, Jaresh-Inyo is hesitant to act in the absence of concrete evidence.[2]
Sisko is confronted by a Changeling in the guise of Miles O'Brien, a DS9 crew member. He tells Sisko there are actually only a total of four Changelings on Earth, and mockingly points out to Sisko how much panic they have caused, drastically out of proportion to their actual numbers.
Sisko contacts Major Kira, second in command on DS9, to uncover the evidence Jaresh-Inyo needs: a Starfleet officer on DS9, Lieutenant Arriaga, has been manipulating the wormhole at Leyton's behest to create the impression that a cloaked Dominion fleet is en route to Earth. Before he can present the evidence to Jaresh-Inyo, Leyton has Sisko framed as being a Changeling and imprisoned. Odo breaks Sisko out of prison.
The crew of DS9 is en route to Earth on the USS Defiant, bringing Arriaga to confess to the conspiracy. In order to prevent Arriaga's evidence from reaching Earth, Leyton orders the USS Lakota to intercept, telling the crew that the Defiant is crewed by Changelings. When the Lakota fires on the Defiant, Lt. Cmdr. Worf, in command of the Defiant, has no choice but to return fire. Outmatched by the Defiant's superior armor and firepower, the Lakota is on the brink of destruction when Leyton orders them to destroy the Defiant. As Sisko confronts Leyton with a phaser, the captain of the Lakota, Captain Benteen, refuses orders to destroy the Defiant and stands down, allowing the Defiant on its way. With his conspiracy falling apart, Leyton resigns, and the state of emergency is lifted.