The Enterprise arrives to assist in solving the crisis of a threatened world whose molten planetary core is solidifying, which will ultimately render the planet uninhabitable. One of the scientists on the planning team, Dr. Juliana Tainer (Fionnula Flanagan), turns out to be the ex-wife of Data's creator, Dr. Soong. Data never knew this woman existed, but she certainly knows him; she helped Soong create him all those years ago, so in a sense she is Data's mother.
"Inheritance" is probably the best installment in the ongoing series of seventh season's Family Tree Theater. It tells an insightful character story about some of the particulars of Data's backstory, which by this point in the series have been sufficiently traveled, but benefit here from a new perspective from a different individual. The always reliable Fionnula Flanagan is good in the role of the former Mrs. Soong, revealing a woman who once shared the passion of creation that Soong did, but lost that zeal after the catastrophic failure that was Lore.
Indeed, Tainer's guilt over how Lore turned out and how that subsequently affected her decision to persuade Soong to shut down and abandon Data — which results in a whole new round of guilt now that she comes face-to-face with him — is evidence of the complexity of the issue of responsibility faced in the realm of artificial intelligence. "Inheritance" benefits from these two characters simply sharing their knowledge about their life perspectives, including brief but effective dialogue where Data reveals his own doomed attempt to create his daughter Lal. (I could've done without the trite backstory that wants to be earnestly and maternally cute, about an early version of Data's programming who refused to wear clothing.)
There's a twist in "Inheritance" as well, where Data discovers, by way of an accident, that Tainer herself is an android that Soong created when his flesh-and-blood wife died. But she doesn't even know she's an android. Soong was able to transfer Tainer's real memories into an android body that is in every way a perfect replica of a human being — right down to medical scans that reveal living tissue at first glance, and especially the fact that this body ages and will eventually die. (There's a subtly nice detail during a violin performance where Data picks up clues that Tainer might actually be an android even before this accident proves it.) And then there's the interactive message left by the late Dr. Soong himself, who explains to Data his intentions and wishes. Enlightening stuff.
This all comes down to a choice that Data must make: Should he tell Tainer the truth — that she is an android — or let her continue to believe that she is the woman named Juliana that she has always believed herself to be? What would you do? And if you were Tainer, would you want to know? Data ultimately decides to allow Tainer to continue believing to be what he himself has always striven to become — a human being. Given such a binary choice, the android Data is able to make the most human (and, for my money, most merciful) of the two options.