The Brides of Dracula

Prologue: "Transylvania...land of dark forests, dread mountains, and black
unfathomed lakes. Still the home of magic and devilry as the 19th C draws
to its close. Count Dracula, monarch of all vampires, is dead, but his
disciples live on to spread the cult and corrupt the world."Marianne Danielle [Yvonne Monlaur] is a student teacher on her way from Paris to the
Lady's Academy at Bachstadt. When the coach makes an unexpected stop
before reaching the Academy and then leaves without Mlle Danielle while
she is getting a meal at the local inn, she is forced to secure lodging
for the night. Unfortunately, the inn is full. That is, until the Baroness
von Meinster [Martita Hunt] appears and offers lodging for the night at her castle.
Suddenly, the innkeeper has a room, but Marianne decides to take up the
Baroness's hospitality and goes to the castle.As she prepares herself for dinner, Marianne looks out the balcony
window and sees a young man on the balcony below. Thinking that the
baroness, the servant Greta [Freda Jackson], and herself are the only ones at the castle,
she wonders who the young (and handsome) man might be. The baroness
confesses that it is her son, the Baron von Meinster [David Peel], who is suffering from an undisclosed illness.
Later, as Marianne prepares to sleep, she again looks out the window
and sees the young man, this time walking on the ledge of his balcony.
Certain that he is about to jump to his death, she calls out to him. She
runs downstairs to his room and learns that he could not be contemplating
a jump for he is imprisoned in his room by an anklechain. Horrified,
Marianne rifles through the baroness's desk in search of the key, which
she tosses to the baron.The next morning, Marianne is found lying in the forest by Dr van
Helsing [Peter Cushing] who accompanies her to the school, even vouching for her when the
schoolmaster accuses her of being tardy. On the way, however, they first
stop at the inn where a young girl is lying in state with two piercing
wounds on her neck. Ever the quintessial vampire hunter, Dr van Helsing
immediately recognizes the nature of the bites and realizes that Marianne
is also in jeopardy.While Marianne is being shown around by student teacher Gina [Andree Melly],
van Helsing returns to the inn where he finds the local priest and
the father of the dead girl arguing over her burial in the churchyard.
That night, van Helsing watches over the dead girl's grave. He finds Greta
lying on it, calling to her. The dead girl works her way to the surface
but, before van Helsing can stake her, she changes into a bat and escapes.
Van Helsing pays a visit to the castle, hoping to encounter the baron, but
instead he faces the baroness, now a vampire, thanks to her loving son. To
release her, van Helsing drives a stake through her heart.Meanwhile, Marianne is making her way at the school. She has a
caller...the owner of the school, none other than the Baron Meinster, and
he asks her hand in marriage. Everything sounds dreamy until the baron
shows up in Gina's bedroom, seduces her, and turns her into a vampire.The baron and his two brides are holing up at the old windmill, so
van Helsing pays them a visit. A fight follows in which van Helsing is
bitten by the baron. To rid himself of the curse, van Helsing cauterizes
the marks on his neck with a hot branding iron. While van Helsing recoups,
the baron fetches Marianne. Again, a fight breaks out, van Helsing
sprinkles the baron with holy water, and the baron kicks over a grate of
burning coals, causing the mill to catch on fire. As the baron tries to
flee, van Helsing leaps on the windmill and moves it just enough to form
the shadow of a cross on the ground below, trapping the baron and
destroying him. [Original Synopsis by bj_kuehl]

Question: What is Baron von Meinster imprisoned by?
Answer: An anklechain