One of my commits is missing

My last commit seems to have vanished, and I wonder if anyone knows where it might have gone.

I had a branch with a big pile of changes on it, and I merged those onto a second branch to tidy it all up and fix one last bug.

I did a git-commit, and then created a third branch to start some other unrelated work (git-checkout -b ...).

Now that second branch no longer has my last commit.

Obviously most of my changes are still on the first branch, but I'd quite like to get back my commit.

Looking through my history I don't see any signs of errant git-reset's so I'm baffled.

Any ideas?

Thanks Luke Diamand