Curate, connect, and discover
I think what really sold Grant Ward being a double agent was that the actor was genuinely acting for the first few episodes. Apparently they only told Brett Dalton about the plot twist the day before filming it so his interactions with the team feel authentic.
I don't think I'll ever be able to wrap my brain around how clever the Ward plot twist is
Bc what the writers do, in regards to a "wolf in the herd", is draw all suspicion off him by having him screw up the past episode. By killing the fake Clairvoyant, "for Skye", the other characters treat him accordingly: he's locked up. He's in a cell when the others learn about HYDRA, and given what he just did, no one (characters & audience) is questioning whether he's really S.H.I.E.L.D.
And so we point fingers at everyone else. Coulson is an obvious no, and unless Skye feels like switching again, she's a no. May feels far too obvious, and Fitz seems as far removed from HYDRA as possible
In fact, the one we all start to suspect is Trip. He only showed up a few episodes ago, and he suddenly gets along with everyone. Not only did he train under Garrett, but he's the one who's with Simmons at the Hub. And everyone is being secretive, everyone's anxious, and Trip certainly doesn't plan on being taken out. Since it's told largely from Simmons' pov during her parts, we're the ones seeing her fear, her cautiousness. Her whole "I can't trust anyone" thing. Trip seems suspicious
And he seems suspicious enough that we don't see the true wolf, the one who's been with the team the whole time