Most of Sleepy Hollow so far has featured Ichabod and Abbie working together to rid the town of its demons, and that's because the show has become a buddy cop drama that requires the two characters in order to succeed. Yet there's merit in separating the two, forcing each of them to figure things out on their own, and that's exactly what "The Sin Eater" does. As Ichabod and Abbie break apart, the show manages to develop their characters by depicting them without their requisite other halves. It's a strong way to spend an hour, especially when that hour is mostly about Ichabod's past before he became a traitor to the British.
"The Sin Eater" begins with a bonding moment between Ichabod and Abbie, which makes it more ironic when they are distanced from each other later on. Abbie tries to explain the reasoning behind her love (and frustration) of baseball - she feels safe, because baseball's rules never change and the game goes on even amid the chaos of the world. Little do they know that a little later, Ichabod will be kidnapped by Freemasons and Abbie will be visited by Ichabod's witch wife to warn of a coming apocalypse because of the ties between Ichabod and the Headless Horseman.
There's some explanation about the bondage of blood between Ichabod and the Horseman when they were reanimated by Katrina, but that's sort of been left up to the viewer to keep straight. Sleepy Hollow has never had an entirely well-defined plot about how Ichabod has come back from the dead to bring the Horseman with him, but "The Sin Eater" works to clear some of that up: it turns out Ichabod harbors a sin from when he was still with the British.
When Ichabod is kidnapped, he's taken to a Freemason brotherhood led by Rutledge (hello James Frain, you've been making the rounds on Grimm and now Sleepy Hollow!), who questions him thoroughly. Apparently some other people have been trying to say that they're Ichabod (eh?) and he wants to make sure this is the real deal. Then Ichabod tells the tale of one of the reasons why he's bound to the Horseman; back when he was with the British army, he tortured Arthur Bernard (Tongaya Chirisa) to try to make him reveal the identity of the pamphlet-writing Cicero. Eventually, Bernard convinced Ichabod that the British were all a bunch of demons, that he should defect to the American army, and that Katrina could save him if he uttered a few words in Latin. But Ichabod's reticence to join the American side ends with the murder of Arthur Bernard, a death he has carried on his chest for centuries.
Meanwhile, Abbie and her sister Jenny attempt to track down a sin eater who can get rid of Ichabod's guilt, thus taking the onus off of Ichabod that he has to kill himself to stop the Horseman's ride. What works about this episode is that, despite some confusing exposition about Horseman bondage and sin eaters, Abbie and Jenny get to sort out their differences without Ichabod while Crane gets to discuss his history without Abbie. We don't normally get to see one without the other, and there's an added tension of seeing them separated, because Abbie is normally the physical one while Ichabod does most of the thinking. In "The Sin Eater," that idea is reversed.
Seeing Ichabod's backstory is actually more fascinating here than any talk of the Horseman. The story about sin manages to include how Ichabod met Katrina, how he defected to the Americans, and shows that he wasn't always the nice guy he has become in present day. A lot of this is wrapped around exposition, but the crux of the matter is that Sleepy Hollow is finally trying to make Ichabod into a character with some depth to his background. And separating him from Abbie means that their bond becomes stronger as well.
It's a good episode, but one that is held together by some questionable mythology. The sin eater takes away Ichabod's sin and, I guess, places it on himself. The easiest possibility to end the Headless Horseman's apocalyptic ride would probably be to kill the sin eater and rid the world of the bond, but I don't think that's an option. "The Sin Eater" leaves a lot up to interpretation, and it also requires the audience suspend disbelief in order to allow the story to progress. That's fine with me when we get such a strong character-driven episode, and it looks like the next episode is going to put all of this one's developments into play.