Showing A Matter of Taste by Fred Saberhagen

Matthew Maule, no stranger to revenge, unexpectedly encounters enemies bent on his destruction for events now over five hundred years in the past—events revealed on a tape found in Uncle Matthew’s Chicago apartment.
For a time, only the Southerlands and Joe Keogh stand between the poisoned and incapacitated Uncle Matthew and his attackers.
But Uncle Matthew is not one to easily surrender his existence.
A tale of revenge and honor.