In music theory, there's a series of notes called a tritone interval. (I'm a writer and a Rock Band player, not a musician, so bear with me, band members.) The tritone consists of three different whole tones: The first sets the stage, marks the spot on the musical scale that our ear can attune itself to. The second note is actually dissonant - it throws off the harmony, and introduces new elements so distasteful that the chord used to be called "The Devil in Music."

The third tone, however, finishes off the chord in exactly the right way, and brings resolution to all of the dissonance. Leonard Bernstein famously put the tritone to great use in the song "Maria" from West Side Story: "Ma-" is the beginning tone, "-ri-" shakes things up with some disharmony, and "-a" resolves the melody, justifying the lead couple's forbidden love.

Now, using that theory to talk about Blizzard's StarCraft 2 trilogy is a little unfair. The second campaign, Heart of the Swarm, isn't anywhere near "distasteful." But it does introduce plenty of new elements to the series, spinning off the RTS classic into places that Wings of Liberty never dared to go. And like that second note of a tritone, it makes sure to leave plenty of ambiguity and promise out there, making sure we're all ready for the big finale in Legacy of the Void.