Fridays at 9 p.m. on Fox. Twelve episodes into the fourth season.
The best thing about science fiction (or any fantastic genre) is how escaping the confines of a strictly realistic setting allows the storyteller to address real issues from a fresh angle. Aliens, for example, aren't necessarily all that compelling in and of themselves (I faithfully watched seven years of The X-Files, where the little green men or gray men or black oil slicks or whatever were nearly always the least interesting things on screen, so I know this for a fact), but aliens as a vehicle for addressing how people deal with the unknown, or how majority groups deal with minorities, or how we conceptualize humanity—that's compelling. Idle fancies can be fun, but the best speculative fiction ultimately returns to earth.
Initially, Fringe was a textbook example of idle, empty science fiction: a facile yet muddled X-Files rip-off in which a top-secret division of the FBI investigates strange paranormal events while powerful shadowy figures manipulate them and their results—diverting enough but hardly promising and extremely derivative. But then, improbably, the writers settled on a brilliant explanation for the paranormal "fringe events": the slow collision of two parallel worlds. With that essential conflict at its core, Fringe has developed a gorgeously baroque mythology and, even better, used it as the foundation for thoughtful, poignant explorations of identity and personal history and guilt and love. In short, when it was just about creepy things going bump in the night, Fringe was dull; now that it's given those sci-fi elements real resonance, it's perhaps the most underrated drama on TV.