This is a Cayman Islands Postage Due Cover. It was sent to Ernest Panton, the Cayman Postmaster, from Barbuda (Antigua) on 5/13/1933.
This cover has some interesting things on it. For starters, it has the commemorative Antigua 1/2d SG 81. It was charged POSTAGE DUE upon arrival in Cayman Islands. This was paid for by 2 1/2d stamps, SG 70, and a 1d Stamp, SG 72.
This item is over $100 USD so I will ship it using Priority Main in the US, and Registered Mail overseas. This is to ensure that it reaches you in a safe and timely manner.