When characters hold back

I'm doing minor revisions to a work in progress, and for the most part it's going swiftly and smoothly. But there's one scene that begs for tinkering--and then a little more tinkering--and then a little more ...

It doesn't help that the main character in this scene is confused, guarded, defensive, frightened, angry, and suspicious. With all that, I have plenty of material on which to build. The problem is that in every pass through the scene, he reveals a little more, which takes the scene in ...