No show on television is as fascinating to follow as BBC's Doctor Who, and Saturday's mid-season finale, "A Good Man Goes to War," proved why. The episode brought back a number of characters from past seasons as the Doctor called on old debts to help him in his quest to rescue the kidnapped Amy Pond and her new baby, Melody.

But that's not all. The episode also answered the single biggest mystery on Doctor Who: Who is River Song? Viewers first met the enigmatic companion of the Doctor played by Alex Kingston three years ago in season 4, when she died. Due to the show's complex time travel, River and the Doctor are in opposite timelines, so the first time he meets her is the last time she meets him. River has always warned the Doctor against spoilers, not giving away too many details about who she is and what her connection to him is.

At the end of the latest episode, that mystery was finally revealed. It turns out River Song is actually Amy and Rory's daughter, Melody Pond (the fact that both names use musical and water imagery is a dead giveaway).

The reveal was the culmination of one of the best Doctor Who episodes ever as war was declared on Amy's kidnappers, who wanted to use her part-Time Lord baby as a weapon to fight against the Doctor (the baby is part-Time Lord because she was conceived in the TARDIS).

The Doctor and Rory traveled through time, collecting old friends and foes who owed the Doctor a debt, and then made their way to Demon's Run, so named because, as the saying goes, "demons run when a good man goes to war." That's exactly what happened, and the show reminded everyone that messing with the Doctor's companions is never a good idea.

The specific details of the invasion were great, but the ending is what truly makes this a very special episode of Doctor Who. The Doctor was tricked and the baby was stolen, but when River showed up and showed the Doctor the truth, his joyous reaction was priceless. His promise to Amy that her baby would definitely be safe was a lot easier to make when you know that she grows up to be River Song.

Perhaps the most ingenious part of the episode, and the reason I'm completely in love with Doctor Who, is that the reveal doesn't end the story. Yes, River is Amy's daughter, but we still have a lot to find out about her relationship with the Doctor, why she's in prison and what the one-eyed Madame Kovarian's plans for her are.

Doctor Who flawlessly answered the single biggest mystery in the show's history without losing any of the storyline's momentum, and I can't wait for the show to return to BBC America at the end of the summer (and not just because the next episode is called "Let's Kill Hitler").

It may be British, but any American not watching Doctor Who is missing out on one of the best shows on TV, sci-fi or otherwise. Not since the heyday of Lost have I been this energized and enthralled by an ending, and I only hope Doctor Who is around for a long, long time.

(Image courtesy of BBC America)