The Enterprise returns to Earth when it is discovered that aliens visited the past and the evidence includes Data’s head! They travel to the planet they think the aliens are from and only Data in the end can see them. While he ends up being sent to 1893 and looks for the aliens, the Enterprise tries to figure out why the aliens might be going back to their history and if it’s a threat. Guinan plays a central role here, telling Picard in the present that he must go on the away mission while Data recognizes her in a newspaper and goes to meet her in 1893. Soon the away team is able to create a device to see the aliens and find that they are killing people in the 19th century. The team follows the aliens through a portal back to 1893 where they are eventually rejoined with Data and meet Guinan. After an encounter with the aliens, an explosion causes Data’s head to be removed from his body and Guinan is injured. Everyone accept Picard travels back to the present and the Captain sends a message to his team with the solution to their problem using Data’s head which they reattach in the present!

There are a lot of great things about this episode. It’s interesting to see Data consider his own demise and it’s nice to get a glimpse into Guinan’s past. Given her longevity, it’s fun to see what she’s been up to during this time and of course see her deal with knowing what’s happening in the present but unable to tell anyone for fear of changing things. Seeing Data’s head contain the solution was also a great idea to tie everything together, using the catalyst that started all this to end it.