Jorja Fox’s Sara Sidle leaves “CSI” Thursday night. No matter how you feel about that development, the episode is tremendous. All actors who depart long-running series should receive such heartfelt, memorable sendoffs.

The episode, titled “Goodbye & Good Luck,” skillfully makes you feel Sara’s disillusionment. She witnesses an eerie case of domestic abuse and remains strangely remote.

But the real crisis for Sara arrives with the return of Marlon West (Douglas Smith) and his genius little sister, Hannah (Juliette Goglia). Last time out, Marlon got away with murder with Hannah’s help. This time he is implicated in a young woman’s plunge from her dorm room.

In the previous case, Hannah got under Sara’s skin. The show has brought back the little girl to needle Sara again. Goglia pulls off her task brilliantly.

As Sara seeks justice, the episode takes turns that are clever or harrowing. Can she finish the case?

The cinematography heightens the Sara’s nightmarish estrangement. “CSI” has won fans as a smart procedural, but the show also can present the personal in vivid terms. Fox plays Sara’s sadness with such wrenching and relatable feeling that this episode becomes an instant classic.

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