The Corbomite Maneuver (Star Trek)

On stardate 1512.2, the Federation starship USS Enterprise, commanded by Captain James T. Kirk, finishes a third day of mapping stars, when novice navigator Lt. Dave Bailey (Anthony Call) spots a large spinning colored cube floating in space. First Officer Spock orders Helmsman Sulu to sound an alert.
Down in Sickbay, Chief Medical Officer Dr. McCoy is giving Captain Kirk his quarterly physical exam. McCoy notices the flashing alert light, but does not mention it to Kirk. Spock calls to inform Kirk about the cube, which is maintaining its position relative to the Enterprise. Kirk is annoyed that McCoy didn't mention the alert, but McCoy stubbornly states that he isn't about to jump and panic over every alert.
On the bridge, Chief Engineer Scott studies the cube, but is at a loss as to how it works. A nervous and inexperienced Bailey advocates attacking it with phasers. Kirk arrives and instead orders the ship to back away from the object. The cube responds by coming even closer and emitting harmful radiation, and Kirk destroys it.
In Kirk's quarters afterward, Yeoman Rand brings Kirk an unappetizing salad, as per Dr. McCoy's medical orders. McCoy tells the Captain he restricted his diet because he has gained weight. In the midst of a series of attack drills, Sulu overrides the simulations, and Spock informs the Captain that a much larger object is rapidly approaching.
Responding to the object's destruction – which the crew soon learn was a boundary marker – a gigantic glowing sphere quickly approaches the Enterprise. It fills the bridge viewscreen, even at low magnification. The vessel's controller, Commander Balok, identifies his ship as the Fesarius, the flagship of the "First Federation".
Mr. Spock manages to get a visual of Balok, a grotesque, blue-skinned humanoid with a frightening face. Balok ignores Kirk's greetings, and announces that he will destroy the Enterprise for trespassing into First Federation territory and destroying the marker buoy. Balok informs the crew they have ten minutes to pray to their deities before their demise. Bailey gives in to his fears, ranting irrationally, and Kirk orders him off the bridge.
Mr. Spock compares the situation to a game of chess: "In chess, when one player is outmatched, the game is over." He regrets that he can find no logical answer. Kirk replies that the solution is not chess, but poker. He bluffs, telling Balok that the Enterprise has incorporated into it a protective substance known as Corbomite which, when the ship is attacked, creates an equal force rebounding on the attacker.
Apparently falling for the ruse, Balok does not destroy the ship as previously announced. During the pause, Bailey, now calmer, returns to the bridge and requests to return to his station, to which Kirk agrees. Afterward, Balok makes direct contact with the Enterprise, requesting details on the Corbomite device. After allowing sufficient time, mostly to cause Balok to worry the details, Kirk refuses.
A tug ship then detaches from the Fesarius and tows the Enterprise deep into First Federation space, where Balok announces he will intern the crew and destroy the Enterprise. Under tow, Kirk orders the Enterprise to increasingly resist the tug ship's tractor beam. Just as the Enterprise '​s engines are about to explode from the overload, it breaks free. This disables the alien vessel. With the power supply nearly drained, the tug cannot even call for help from the bigger ship.
Rather than flee, Kirk, McCoy, and Bailey form a boarding party to render assistance. Spock remains on the Enterprise to assist them, if this was a trap. Scott, operating the transporter, tells them to bend down, as the scan of the alien ship reveals it has a low ceiling. Upon arrival they discover that the "Balok" who appeared on their monitor is just a dummy, and the real Balok resembles a hyperintelligent human child. He enthusiastically welcomes them aboard, offering them "tranya", his favorite beverage.
Balok explains that he was merely testing the Enterprise and its crew, to discover their true intentions. Although he had read the Enterprise computer records, he felt they could have been a deception. He created his dummy alter-ego, as he knew his true appearance would never frighten anyone.
Kirk and company finally relax. Balok says that he runs the Fesarius entirely by himself and greatly misses company and conversation. He expresses his desire to learn more about humans and their culture, and Lt. Bailey is volunteered by Kirk to remain on Balok's ship as an emissary of the Federation, an assignment Bailey happily accepts.