So you've just finished the first book in a series and loved every minute of it. You immediately run out and pick up the sequel, hoping it will be just as good.

But what's this? The heroes are on the run from the bad guys? But they won in the first book! And why did the hero and his girlfriend break up? What the hell is going on here?

What you have here is a Left Turn Sequel - a sequel that breaks assumptions that the reader made based on the ending of the original. This may involve some kind of Plot Twist, but it doesn't have to, and not any Plot Twist would qualify either. If your first reaction to a sequel is to do a double-take or say "What the hell?", there's a good chance that it's a Left Turn Sequel.

May involve a Retcon, although it doesn't have to.

Note that a Left Turn Sequel isn't necessarily a bad thing - many Left Turn Sequels turn out to be worth successors or even Surprisingly Improved Sequels. After all, plenty of stories end with a victory that seems a little too convenient when you think about it - The Empire may not fall just because you killed The Emperor (unless...).

If the left turn undoes the changes of the previous work, you have a Sequel Reset. See also Sequelphobic, which is a common reaction to a sequel that sounds like it might fall under this trope.

As a trope about endings, BEWARE UNMARKED SPOILERS!

Do We Have This One? There doesn't seem to be a clear match under the Sequel tropes, but if it isn't indexed...

• The Empire Strikes Back opens with the Rebel Alliance in dire straits, despite the fact that Star Wars ended with a major victory for them. The EU also contains too many stories to count that involve some new leader taking Emperor Palpatine's place after Return Of The Jedi.
• Starcraft ends with the destruction of the Zerg Overmind. Earlier in the story, the death of the Cerebrate Zsaz weakened his Zerg brood and made them a danger to the rest of the Zerg Swarm, but in Brood War the leaderless Zerg are apparently more dangerous than ever and proceed to destroy most of Aiur. Nice Job Breaking It Hero.
• In the Foundation series, the ending of Second Foundation implies that the Seldon Plan is back on track. Later sequels reveal that it didn't actually work, and that it doesn't matter anyway because the Seldon Plan is fundamentally flawed.