Murder Becomes Mayfair

A mild-mannered tailor working on Savile Row is found shot to death in a wooded corner of Hanover Square in London. On his corpse is the 'calling card' of The Organization, which confirms they committed the murder and are set to launch their next terror plot.
But what form of terror do they have in mind this time, why was their execution of the tailor necessary, and who within his inner circle committed the crime?
Upon arriving in London, architect/detective Dalton Lee and his team come upon an abundance of suspects with both the motive and opportunity to have ended the tailor's life. Can they deduce who pulled the trigger before The Organization succeeds with their sinister scheme?