TOS Season 2 Episode 6 The Doomsday Machine

Plot

The USS Enterprise, following a trail of mysteriously destroyed star systems, picks up the automated distress beacon of one of Enterprise's sister ships, the USS Constellation. Upon arrival, the Constellation is found heavily damaged and drifting in space; Captain Kirk, Chief Medical Officer Dr. McCoy, Chief Engineer Scott, and a damage control team transport to the ship to evaluate her. There they discover the only member of the crew still aboard: the ship's commander Commodore Matt Decker, who is suffering from severe mental shock.
After McCoy injects him with a sedative, Decker explains that he and his crew had discovered a giant machine, miles long, that used beams of antiprotons to tear planets apart, consuming the rubble for fuel. The attack by Constellation on the machine was ineffective and the ship suffered heavy damage. Decker evacuated his crew to one of the planets of the system, which the machine subsequently destroyed. Kirk theorizes that the machine is an ancient doomsday machine, which must be stopped before it reaches more populated sectors of the galaxy. McCoy and Decker transport to Enterprise, which has taken Constellation in tow, while Scott's damage control team attempt repairs on Constellation's damaged impulse engines, weapons and shields. Kirk attends to Constellation's nonfunctional viewscreen, which, aside from communications from Enterprise, will be his only means of monitoring events outside the ship.
Enterprise's first officer, Spock, informs Kirk of the sudden appearance of the so-called planet killer and it begins to pursue Enterprise. As the boarding party prepares to beam back aboard, the machine attacks Enterprise, damaging the transporter and disrupting communications. Decker, now the senior officer on Enterprise, assumes command and orders a phaser attack. The phasers are useless against the machine as its hull is constructed of solid neutronium, and the ship is then caught in a tractor beam which draws it towards the planet killer's maw. Kirk completes his repair of Constellation's viewscreen and is shocked to see Enterprise engaging the machine. Scott has managed to repair impulse engines and recharge one of Constellation's phaser banks, so Kirk uses the crippled ship to approach and fire at the planet killer, distracting it long enough for Enterprise to escape its tractor beam. After repairing the transporter and reestablishing voice communications, Enterprise retreats to a safe distance. Spock relieves Decker of command on Kirk's orders and Decker is escorted to Sickbay. However, Decker subdues his security escort and steals a shuttlecraft. Overcome with guilt because of the loss of his crew, Decker informs Spock he is flying the shuttlecraft straight into the maw of the machine. Despite Kirk's plea for him to return to Enterprise Decker does not deviate from his course and dies.
Lt. Sulu reports that the shuttlecraft explosion has reduced the planet killer's power output by a small amount. Realizing that this may have been Decker's intention, and hoping that a starship would do much more damage, Kirk comes up with a plan to explode Constellation inside the planet killer. Over Spock's objections, Kirk insists on piloting the damaged starship himself, and Scott rigs the impulse engines to explode with a thirty-second delay before detonation, warning his captain that once the timer is enabled, there is no way to abort it.
With the rest of the boarding party transported back to Enterprise, Kirk aims Constellation at the maw of the planet killer, triggers the timer, and orders Enterprise to beam him aboard. The transporter malfunctions, and Scott races to set it right with advice from Spock. With virtually no time to spare, Kirk is safely beamed aboard Enterprise as Constellation explodes inside the planet killer, leaving it dead in space, its threat ended.