Stardate 45959.1/46001.3: The Enterprise investigates the mystery of Data's head, which was found in a cave in San Francisco, among artifacts from the 19th century. The trace leads to Devidia II where an away team discovers a time rift that transfers Data to San Francisco of the year 1893. Here Data meets Guinan, who has no recollection of him because she will meet him in the future, and Samuel Clemens aka Mark Twain, who is suspicious about the strange visitors. An away team with Picard follows Data and they discover that aliens from Devidia II are consuming energy from cholera victims of those days. Just when the away team are going to leave the 19th century through the cave, they are first surprised by Clemens and then by two Devidians. They open the gateway which decapitates Data. Data's body, the away team and Clemens make it to the 24th century, while Picard stays behind with Data's head. Since the "new" head is in the 19th century (and has to stay there to be found), there is no other way for Geordi but to use the "old" head found in the cave to repair Data. In the 19th century, Picard leaves a message to be found in Data's head that allows Clemens and Picard to return to their respective time.

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