This unique, uncommon cover was sent from the Washington D.C. P.O. to St. Louis, MO, on February 8, 1886, by someone with the U.S. Post Office Department, Office of Foreign Mails! While I cannot be utterly sure, it looks like mail(not present now) from Newstead, Australia(via San Francisco), for a Miss Maggie Pepper/Pesser(?), was enclosed in the envelope. The mail must have somehow come out of its original envelope, making it undeliverable by normal means. While there are no signs of additional postage required, it would make sense that there might have been some required for the U.S Post Office's special service provided in this instance. To be perfectly honest, this is the first example I have ever seen of mail sent from the U.S. Post Office's Office of Foreign Mail!
To continue, outside of damage tear and shorter perfs) caused to its top, right corner due to how the envelope was opened by the recipient, the brown, 2-Cent, U.S., "Washington," issue is in good condition. The duplex cancel from the Washington D.C. P.O. is immaculate! There are two, decent(but smudged and/or lightly canceled/faded cancels) from St. Louis area post offices, one a transit, mark(2/9/86), and the other one from a sub-station, applied on February 10th.
Lastly, as for the condition of the envelope, itself, it's in pretty good shape, overall. It's pretty clean. It has been reduced some due to being opened at the right side. The back flap is 95% intact. Noted imperfections aside, this remains a relatively rare, intriguing piece of U.S. postal history connected to the U.S. Post Office's special Office of Foreign Mails, and the service(s) it provided to senders of incoming foreign mail, that had been undeliverable by usual means!