Enigmatic_Messages

We need you to decrypt this message sent by a group of interest. We know this group has an inside joke about Alan Turing and Bletchley Park. Not sure what the connection there is. Something Enigmatic is happening and there needs to be a stop to it. Our inside man says there is 1 plug in the plugboard, not sure what that means, and using the M3 machine. If it helps at all, the followers begin every message with SIDXTHEXSLOTHXROCKSXSOCKSXZ

The Message is as follows: XTKOFZFRIFWLOESVNSAGZYUJHTXSOHSMHQLNWYGEFVNXNQOMSGJSIEKEQZGPRBQUIJMHIPOVQKOYDOBIFWCIQBJFREQFWTLRXITPTYMUDJWKLWTLWIIZHYOENRGPLBYWKBBEZFHFETJALRFJJNLLEJWWPQDDUEHTNITAIWHYGUPSRZZAPYGLPHCBKFMMQV

NOTE: The flag is encoded like BCCTFZZstuffZZ