[WriterBoy]

/grunch on

This looks like a pretty easy fold on the turn for me. If the LAG is indeed raising/calling with anything, having both the flush out there, plus the straight, plus that many people in the pot, your Top is beat.

/grunch off

edit: blah, i misread the OP. Here's the deal, you bet the turn. However I'm pretty sure that the button has the flush. I think he was checking for deception. If you bet that turn, I think he would raise you. If that is the case, I would fold.