Heir to the Throne was the first campaign for the open source Battle for Wesnoth. In fact, the entire game engine and programming was designed just to accommodate this campaign, so in a way, "Heir to the Throne" was originally Wesnoth. The campaign is still included as one of the game's core campaigns, although it is not quite as central to gameplay as it used to be. Campaigns in general are less central than they used to be, since many players prefer multiplayer games.
The story of the campaign follows the deposed, titular, heir to the throne, Prince Konrad, who has been raised in a distant forest amongst the elves, by a court wizard, Delfador who saved him from his evil stepmother. When the campaign begins, the evil stepmother has found out where they are hiding, and sends her orcish hordes to kill them. The campaigns follows them as they escape, and then gather together an army of various allies, until finally they overthrow the queen in a climactic battle. If this sounds somewhat cliche, it is because it is (although there is one major plot twist along the way. Computer games, like other forms of entertainment, often uses plots that are only meant to provide some probably shell to what is happening. The plot of the campaign is episodic, with different rationales provided for what the current scenario is like. The narration says that while on the run, your party has come to a valley haunted by undead. This is, of course, mostly because the campaign designer wanted to let the player try a new and different strategic and tactical puzzle.
Despite the episodic and somewhat predictable nature of the plot, the campaign is still very good, and challenging, especially for the new player who is still trying to learn Battle for Wesnoth's rules and subtle strategies. Playing through it, even on easy difficulty, can take at least twenty hours.
The main reason I describe this campaign is not just for the few people here who are familiar, or even fans, of the game. To me, the campaign is interesting because it is presented as straight-forward high fantasy, good vs. evil story telling. This was how the game was first experienced by most fans, and it seemed to entertain many of them. And yet, when those fans started making their own campaigns, many of which became official, they made much more complicated, sophisticated campaigns, both in terms of game structure, and plot. Enemies became trickier to defeat, and the plots hinted at more ambiguity: later campaigns would feature orcs as heroes, fighting against human expansionism, for example. But many of the same locations and events in Heir to the Throne were expanded upon with greater complication, somewhat in the manner of a jazz musician improvising on a pop song.