“Legacy” is episode six of season four of Star Trek: The Next Generation.
Troi, Worf, Data and Riker are playing poker. Riker thinks Data has the best poker face he’s ever seen. Troi comments that Riker and Data have successfully divided the evening between them. Worf suspects conspiracy. Not that he’d accuse superior officers. Riker tells Data he’s getting harder to bluff. The says he will find any card in the deck Data choses, and Data will help him find it. He does, but Data saw how he did it. Then Captain Picard contacts Riker; they have received a distress call and are changing course. The Federation freighter Argos has had to take emergency orbit around Turkana IV. Tasha Yar’s homeworld.
On the bridge, they get a subspace message from the freighter. There’ five minutes until a warp drive containment breach. Make that three. The Enterprise increases speed and the captain contacts O’Brien, telling him to be ready. They arrive, but the freighter explodes before O’Brien can beam anyone off. There is an ion trail consistent with an escape pod. It’s heading to the colony, and the colony sounds like it’s in a mess. The last Federation contact was warned anyone heading down would be killed.
Turkana IV is an Earth colony that severed relations with the Federation nearly 15 years ago. There’s no alternative but to beam down. Data, Riker, Worf and Dr Crusher are heading down; the surface colony is destroyed and people are living underground. Worf is concerned for the doctor’s safety. Perhaps she should wait until they signal. She isn’t going to wait.
In the tunnels, they are unmolested then encounter a bunch of armed people who tell them to ID themselves. The people might know where the missing crew are and say to follow, as someone is pursuing them. Back at their base, the leader, Hayne, breaks open a case of stolen synthale. He tells the others the Alliance is keeping the crew hostage; they can expect a ransom. Riker wants to speak to the authorities. The Alliance, and this group, the Coalition, are the authorities. Hayne can help, in exchange for something. Link phasers. The Alliance has recently found weapons and will kill their missing crewmen anyway. Dr Crusher mentions what they’ve heard about the colony and Data talks about Tasha. Riker says they will consider this and orders the Enterprise to beam them back. Hayne wants to know everything he can about the Enterprise.
Captain Picard isn’t going to trade weapons when Hayne contacts the ship. He has someone they might like to meet. Ishara Yar, Tasha’s sister. Hayne has decided to help them, rather than risk the Enterprise being forced to pay a ransom. Ishara will be the liaison and will help them come up with a rescue plan. Worf doesn’t trust her and Riker says she could be a fake. Troi says Hayne is deceiving and hoping to manipulate them and she can’t ID Ishara. The captain accepts the proposal.
Data welcomes Ishara aboard and mentions Tasha. Ishara thinks Tasha was a coward for leaving the colony. Data has never heard that term applied to her. Ishara is escorted to the observation lounge. She says they can take a sample of her DNA if they like. Dr Crusher will. Ishara explains that the Coalition and the Alliance were the two strongest factions during the infighting and the government gave them police powers, with proximity detectors that meant they couldn’t attack the other faction directly. In a few months, they didn’t need the government, Tasha asked Ishara to come with, but Ishara had already joined the Coalition.
A transmission is received from the colony. One of the missing crew states that they have 20 hours to make reparations for the Federation intrusion, or he and his pilot will be killed. Ishara tells them to take this threat seriously. Geordi can use a detector in the escape pod to track the crew more directly. Ishara knows where the pod is being stored.
Ishara helps with a plan to get to the escape pod and Riker discusses the plan with Picard. Data takes Ishara to Dr Crusher for a DNA sample and explains how Tasha died. The captain approves the plan.
Everyone is getting attached to Ishara, because of her connection to Tasha. Ishara herself seems to be getting a different picture of her sister than the one she had in her head. She also seems to like the alternative that the Enterprise represents. Data tells Ishara his definition of friendship.
In many cases, such an episode where a now-gone person is being discussed, there would be clips of said person. Given how poorly “Shades of Gray” was received, the idea of playing clips of previous episodes may have been rejected out of hand.