On first watch, "Pure" left a big impression on me. It really creeped me out and the truth was not expected on the whole. Was also not expecting Martin Short to be so good in such a dark role. Did have doubts about whether he could pull it off as it is the complete opposite to his usual work, but 'Law and Order: Special Victims Unit' proved frequently (as did the franchise in general) that it can have guest stars playing against type and excel.
"Pure" is one such example, and actually one of the finest and most surprising. It is yet another fantastic episode where everything works, and is one of the best ones of one of the show's better overall seasons in my view (with it having such a high number of great and more episodes and with only two that were below good and even they were still watchable). Everything is just so brilliantly executed here in "Pure" that it didn't matter to me at all that one aspect of the plot was not that hard to figure out.
A major reason as to why "Pure" works so brilliantly is the performances. All the regulars are excellent, with Christopher Meloni in particular giving a performance that is as equally riveting as the one he gave in the superb previous episode "Rage". The biggest surprise is Short, showing a completely different side to him. One would never think that he was capable of pulling off creepy, but he ends up giving in my view one of the creepiest guest turns in the history of 'Special Victims Unit' and in a brilliant way.
The dynamic between Stabler and Ballentine has a lot of nail-biting tension, which is sometimes very strong and at other times quite subtle. The story is often very unsettling, a big example being the quite nightmarish opening scene (every parent's worst nightmare) and there are plenty of shocking twists and turns in the second half. It was to me pretty obvious early on that Ballentine knew more than what he was letting on, too many details hinted that were too vivid for what he was saying he was (plus there is a similar plot device in a later episode of 'Taggart' seen well before this, except it is handled a lot better in "Pure"). Actually didn't mind that much as it was executed very well, had a real unsettlement and the things revealed in the second half were truly shocking.
Script is tight and thoughtful, with nothing cheesy or rambling. The production values are slick and have a subtle grit, with an intimacy to the photography without being too claustrophobic. The music isn't used too much and doesn't get too melodramatic. The direction has momentum while being accommodating and strongly creating a dark atmosphere.
In support, superb and what 'Special Victims Unit' is all about. 10/10