This episode really really really rocked. Don't you just love when they work with terrorists? I know i do, because nobody except a terrorist truly understands their minds, which makes it even more interesting watching Don, Charlie and the gang trying to get into their minds to solve the case.
I think it's awesome how they used the sarin, and the waterways to conduct the terrorism. Sarin really is serious stuff, and when the terrorists have mathematical scientists working on their side to figure out dilution factors, it really does make the episode interesting.
But as usual, Charlie uses his maths to figure it out.
And the cop guy being involved, that's just pure cliche and genius.