He was captured and held hostage by Viking invaders, but refused to let his poverty-stricken people pay the ransom for his return, and therefore gave his life for them.
You can read the full story here, told by Fr. Percy Dearmer in a ‘ripping yarns for kittens’ kind of a way.
Alphege was martyred in Greenwich, not far from where we used to live in South London, and he is one of England’s great Saints. Saint Thomas Becket prayed to him just before he himself was martyred in Canterbury Cathedral. (Being Archbishop of Canterbury must be a dangerous job. We shall refuse it when offered.)
Later on, Archbishop Lanfranc (boo!) tried to remove Alphege from the Kalendar, on the grounds that he was not a true martyr, having died for his people rather than explicitly for his faith. But good old Saint Anselm (hurray!) argued that whoever is a martyr for justice and love is a martyr for Christ.
We are pleased to report that, despite being on the side of justice and love, we have not thus far been pelted with any strange missiles. We did, however, spend a pleasant afternoon pelting sweet papers and bits of fish finger about the Vicarage. Ah, happy days.