Bernard Ross (Nicholas Woodeson) is having a crisis of faith and a belief in the existence of vampires after the death of his daughter, Louisa.
She had a strange, unexplained ailment and her grave appears to be disturbed.
Bernard's friend Gilbert Gallamore has brought in fearless vampire hunter Silas O'Hagen. Louisa's aunt thinks this is all poppycock. A sentiment shared by Father Brown.
There is also the curious case of Inspector Sullivan who has fallen ill. Suddenly Mrs Devine discovers he is averse to daylight, dislikes garlic and she cannot see his reflection.
When Gilbert is found dead. Father Brown teams up with Sergeant Goodfellow to investigate.
I did think the presence of the Silas O'Hagen character destabilised the story too much. If he was a con merchant in the locality, it would had been well known to Sullivan, Goodfellow and Father Brown.