Golden Sun: Dark Dawn. Pretty much, the game begins with one plot, goes on a tangent to the main plot, and then picks up the first one again three seconds before the credits. You can't end a game with "to be continued" and then not make a sequel! The same applies to Rhythm Thief, which while working pretty well as a stand alone, had many plot threads left hanging, including one that was obviously pointing to a sequel. Nad a bonus chapter in which one character discovered some huge secret about the bad guys, but then the chapter ends before the player discovers what it is. :/