When a partnership does not play negative doubles or Lebensohl to combat opponents' interference after partner's Notrump opening, stolen bids may come into play. Responder's bids are as follows:
a) Where the opponents have bid the suit responder was going to bid, he doubles. Thus, for example, where the opponents bid diamonds and responder was going to bid diamonds to make a transfer to hearts, responder would double to make the transfer. This works for Stayman as well.
b) When the opponents have interfered, but have not taken responder's bid, responder makes the bid at the cheapest level. For example, if the opponents overcall 2 and responder wishes to transfer to spades, he makes the standard 2 bid. If responder wishes to bid Stayman, he would bid 3 (that's the cheapest level to make the asking bid).
c) other than the 3 bid where Stayman is appropriate, 3-level bids are natural and forcing. (a few don't play it as forcing, but this appears to be the exception)