William FitzAlan was an Anglo-Norman baron and lord of Oswestry who supported Empress Matilda during the civil war known as the Anarchy. King Stephen deprived him of Shrewsbury and his estates after rebellion in 1138, forcing him into a long exile before restoration under Henry II.
He later resumed his position in the Welsh Marches and was associated with the patronage of Haughmond Abbey. William FitzAlan, Lord of Oswestry belonged to FitzAlan. William FitzAlan, Lord of Oswestry is generally dated to 1105–1160.
Ellis Peters’ One Corpse Too Many is set at Shrewsbury in 1138, when the town is caught in the struggle between King Stephen and supporters of Empress Maud. William FitzAlan’s adherence to Maud and loss of Shrewsbury to Stephen form part of the political background to the siege and the mass execution from which Cadfael’s murder mystery emerges.