Ya your right I don't see one. Hard to tell from the picture, but are you sure there isn't a screw or anything hidding under the hard water build up in the front part of the crease in the handle? This one may be a twist off. Sometimes they are threaded on. I've never seen the particular model you have, but if it has no screw and the handle is one piece which it appears to be. I would assume that the beveled cone between the trim plate and the handle must be threaded. Try to turn it counter clockwise and see if it will unthread. They work like that on a lot of lavatory sink and bath tub faucets. I've never seen that design personally on a shower valve, but from the picture that would be my assumption.