Arsenic and Old Lace opens in the living room of the
Brewster home, inhabited by two spinster aunts, Abby
and Martha Brewster, and their nephew, Teddy. Rev.
Dr. Harper is chatting with Abby about her other
nephew, Mortimer, who in love with the reverend’s
daughter, Elaine. Soon joining the conversation are
two friendly police officers, Brophy and Klein, who
have come by (as they often do) to pick up a box for
charity from the kindly Brewster sisters. Theodore,
who is rather crazy but harmless, thinks he is
Theodore Roosevelt and charges up the stairs to
retrieve the box. The reverend and the policemen
leave, only to be replaced by Mortimer, who
announces to his aunts that he intends to marry
Elaine, whom he is taking to a play that evening.
However, the happy family starts to unravel when
Mortimer lifts the lid to the window seat and
discovers a dead body within. He immediately assumes
that Teddy has killed the man. However, Abby and
Martha tell Mortimer that it was they who poisoned
the man with their homemade elderberry wine—and that
he is the eleventh (or twelfth, depending on how you
count) gentleman they have shared their wine with. The
sisters explain that these are charitable acts: They
befriend lonely older gentlemen who do not have much
to live for and then kill them with elderberry wine
laced with arsenic. They continue that Mortimer should
not worry because Teddy is down in the cellar digging
what he believes is the Panama Canal, but is in
reality the latest grave. Just then Elaine arrives and
an exited and worried Mortimer tells her they are not
going to the theatre afterall. After a brief quarrel,
Elaine leaves. About this time, Mortimer and Teddy’s
brother, Jonathan, shows up. Jonathan, a true maniacal
criminal, is accompanied by Dr. Einstein, a plastic
surgeon of doubtful character. Dr. Einstein has changed
Jonathan so that he looks like Boris Karloff, the
horror film star. Teddy invites Einstein to join him in
the cellar, where he is supposedly digging the Panama
Canal. Einstein quickly returns and confides to Jonathan
that there is a hole large enough to bury Mr. Spenalzo
(a man Jonathan recently killed) after everyone goes to
bed. Once the lights are out and everyone is supposedly
asleep, Teddy goes to the window seat to get Mr. Hoskins,
and Jonathan and Einstein go to their car to get Mr.
Spenalzo, both planning on filling the hole in the cellar.
Thus begins several hilarious scenes of lights blinking
on and off, of bodies being moved from the window seat to
the cellar to the car outside, and of accusations and
threats back and forth. Because of the commotion at the
house, Officer O’Hara stops by to make sure all is well.
When he is convinced that everything is alright, he shifts
topics and corners Mortimer in a discussion of a play he
is writing. Just then, Lieutenant Rooney bursts in and
recognizes Jonathan as an escapee from a prison for the
criminally insane. Jonathan tells the officers about the
bodies in the cellar, but they don’t believe him and take
him off to prison. Einstein gets away, and Theodore is
certified insane and taken to the Happy Dale Sanitarium.
Trying to protect society without sending his aunts to
prison, Mortimer ecstatically agrees when his aunts insist
on going to Happy Dale with their nephew. The aunts then
kindly inform Mortimer that he is actually not a member of
the Brewster family. He was an illegitimate child and thus
can marry Elaine without fear of passing the Brewster
insanity on to his children. Mortimer happily departs, but
before the women leave their house, they offer a drink to
the head of Happy Dale, Mr. Witherspoon. Witherspoon is a
lonely older gentleman, and he gladly accepts a glass of
the spiked elderberry wine. . . .