Pere Artist was at the time of this story working in the dark blue bit of MoD with the rank of Commander. He went to a meeting with some green jobs in the green bit and left behind his fountain pen at the end of the meeting.
A day or so later a green job WO rang him. "You left your pen behind after your meeting with Colonel Green, Sir, so I brought it to your office earlier today. You were out, so I left it with your assistant Captain Smith."