This is a St. Lucia Postage Due Cover sent from St. John's, Antigua to Castries, St. Lucia on 6/5/1932.  It has a St. Lucia Receiver on the back dating 1/21/1932.

An Antigua stamp, the 1/2d Green was used as postage, but the real thing of value on this cover is the pair of St. Lucia POSTAGE DUE STAMPS, The First Issue SG D1, the 1d.  These are #13694 & 13684 and cancelled 5/15/1932. 

Additionally, this cover has a BLACK ANTIGUA TERCENTENARY YEAR CANCEL!  

These little guys are valued at L48 x 10 = L480, according to the Stanley Gibbons Catalogue!

This item is over $100 USD so I will ship it using Priority Mail in the US, and Registered Mail overseas.  This is to ensure that it reaches you in a safe and timely manner, and includes tracking!