Mr Angel is a non-canonical character, created for the 2022 miniseries Why Didn't They Ask Evans?, an adaptation of the Agatha Christie novel of the same name. He a mysterious, suspicious man whose name is not known until the end of the third episode. He is first introduced at the mass imminently after Pritchard's death, then appears to be following people around, looking for Bobby Jones.
Spoiler warning: A spoiler is announced! The following section contains details about the plot of Why Didn't They Ask Evans?.
At the end of the third episode, he is unmasked as Moira's henchman (along with the Caymans), a hired man from Netherlands who has been doing some of the dirty work for her and Roger Bassington-ffrench.
Spoilers end here.