So I'm in part 2, at the part where the Shadesmar expedition just got off the boat to resupply, and Shallan contacted Mraize and found out Beryl is the spy.
But I'm going to make a prediction that not only is this a misdirect, ALL of the humans are a misdirect,and the spy is actually one of the spren somehow. No idea how they'd have off'd Ialai, though.