Symbolism, Imagery, Allegory
A Passage to India? Nope, Just to a Creepy Lab.
We start off with the story of a door in a rough neighborhood that leads to a passageway that leads to Dr. Jekyll’s laboratory.
Which, as it turns out, is a great place to start a novel that is heavily preoccupied with the idea of "leading to." Dr. Jekyll's strict adherence to Victorian morals leads to his desire to act out, which leads to his creation of an alter ego, which leads to Mr Hyde having tons o' fun being an evildoer, which leads to Dr. Jekyll losing control, which leads to a final, desperate act of suicide.
This book is basically a Rube Goldberg machine of consequences.
And this passage is also a passage between two worlds. Until the end of the story, Jekyll (himself and as Hyde) is the only one who traverses this passage. He’s also the only one walking the fine line between normality and evil. Sounds like a symbol to us.