To cut a long story short, I was trying to remember which Byzantine emperor it was who was murdered at Christmas Mass. Upon looking it up, the answer is Leo V, and... actually, I'm just going to c+p the whole Wiki bit because oh my days, there is TOO MUCH going on here. Every single sentence just builds on the last:
The conspiracy which was to overthrow Leo was led by the Domestic of the Excubitors, Michael the Amorian, who disapproved of Leo's divorce and remarriage (he was married to the sister of the divorcée). In late 820, agents of the Postal Logothete uncovered the plot. Leo imprisoned him and sentenced him to death by burning, but Empress consort Theodosia arranged a postponement of the execution until after Christmas.[2]: 433  This allowed Michael to organise plotters to carry out the assassination of the Emperor in the palace chapel of St. Stephen on Christmas Eve. Leo was attending the matins service when a group of assassins disguised as members of the choir due to sing in the service suddenly threw off their robes and drew their weapons.[20] In the dim light they mistook the officiating priest for the Emperor and the confusion allowed Leo to snatch a heavy cross from the altar and defend himself. He called for his guards, but the conspirators had barred the doors and within a few moments a sword stroke had severed his arm, and he fell before the communion-table, where his body was hewed in pieces. His remains were dumped unceremoniously in the snow and the assassins hurried to the dungeons to free Michael. Unfortunately for them Leo had hidden the key on his person, and since it was too early in the morning to find a blacksmith, Michael was hastily crowned as emperor with the iron clasps still around his legs. Leo's family (including his mother and his wife, Theodosia) was exiled to monasteries on the Princes' Islands. His four sons (including ex co-emperor Symbatios) were castrated, a procedure so brutally carried out that one of them died during the "operation".[21]
