Jekyll and Hyde - Season 1 Episode 8 -

Robert has no wish to find the monster that is killing wealthy young men, but the trail is too compelling to resist. It leads him to a fight with a beautiful vampire who shocks him with the news that she's his sister, Olalla. She also tells him Dance is alive and being rebuilt by eel creatures. Robert is suspicious of a trap and sets a test - if she can turn into a Jekyll he'll believe her.