There are a number of inheritors to a fortune who are getting killed by a mysterious somebody whom we do not see. Each death is novel, but not terribly graphic. Who did it?

Alboino, the Lombard ruler, wants to marry the daughter of a neighboring king, but she loves another. Her father arranges the marriage to Alboino, which he believes will be beneficial to him, only to have Alboino kill him and leave Amalchi, his daughter's real love, beaten and left for dead. Amalchi recovers to lead a revolt against the murderous Alboino and reclaim his woman.