Star Trek: The Next Generation: "Time's Arrow, Part II"

It is 21 September 1992, and time for the sixth season premiere of Star Trek: The Next Generation.

Trapped in 19th century San Francisco, Captain Picard (Patrick Stewart) and his crew must defeat a pair of shape-shifting aliens that are murdering innocent people in the streets, as well as find a way back to the 24th century, with the help of a young Guinan (Whoopi Goldberg) and author Samuel Clemens (Jerry Hardin).

There is a trick to a good time travel story, and that is to establish your rules early and stick to them throughout. There are basically two kinds of time travel story along these lines. The first is one where travellers to the past can change the future, and eventually arrive home to find a transformed world. The second is one where travellers to the past change nothing at all - all of their actions in the past have simply formed part of a history that was always there. Hollywood tends to favour the former (think Back to the Future), but to be honest I am always a more enthused fan of the latter. "Time's Arrow, Part II" typifies this second approach.

The first part of this storyline kicked off with a mystery: a disused and sealed-off San Francisco mine, soaked in alien radiation, and containing a fobwatch, a revolver, and Data's severed head. Much of this second part's action leads into showing exactly how all three items came to be there. History does not get changed, and Data's decapitation is not averted. There is a particular kind of ludicrous genius to the idea that the Enterprise crew return to the 24th century via the alien portal, with Data's head getting severed and left behind in the process, and Geordi (LeVar Burton) simply taking the 500 year-old head they retrieved from the cave and re-attaching it to Data's body. It eventually works, Data is revived, and the character continues to appear in another two seasons and four feature films with a head five centuries older than his body.

Overall the episode is divided into two halves, and while generally excellent it does feel like a bit of a rush. The first half sees Picard and his crew already settled into San Francisco for some days, living in a boarding house and masquerading as police officers, nurses and other 19th century workers. It does not take them long to reunite with Data and track the aliens back to the mine where they have set up their time portal. It is all undertaken at a remarkable speed, cutting out any non-essential material to reach the second half of the episode.

That second half sees Picard left behind in San Francisco when Guinan is injured, and Clemens in the 24th century visiting the Enterprise. While a little of Hardin's Clemens goes a long way, the same cannot be said for Picard and Guinan. It is a critical meeting between the two - the first time Guinan ever meets Picard in her timeline - and it feels rather short-changed compared to what it could have been.

A third part for this story would have done a world of good. There would have been time to better showcase the Enterprise crew living in San Francisco, to explore the alien predators sneaking around in the past, to properly establish Picard and Guinan's meeting, and so on. This is a good episode - in fact it's a rare second half of a Star Trek two-parter that generally matches its first - but the potential to be even better is all over it. At any rate, good is good: Season 6 launches to a promising start.