Very hard decision to make without an inkling of South's Bridge Ability. All things being equal, South should have no more than 6 HCP. I find it hard to fathom South's distribution to be some variation of 1-2-5-5. He did not try 2n originally and West's failure to support and failure to bid 1S suggest at least 8 cards in the minors. One possibility might be a massive 5/6 or 6/5 hand by opener with sketchy reverse count. West must have a couple of spades anyway on the bidding which does not reveal the likely hood of a spade stack in south. I think the most likely scenario is that East has opened a very distributional hand with less than reverse count. South has a good 4 card Spade suit which his bidding style precludes him from showing at his first turn. South thinks that N/S may be on the way to game and is suggesting a defensive plan. West's pass of the double clouds this reasoning somewhat, but assuming I was able to make all these deductions in a timely manner, I would pass.
