A main disruptor of the Victorian domestic spaces in this novel is Tonga, the mysterious "other." As is eventually revealed, he is a native of the Andaman islands off India. In highly racist depiction, he is called a "black cannibal." He is described as very small and kills people through the use of a poison blowdart gun, even though native groups near India did not, in reality, use this form of weaponry.

Watson, a symbol of British normalcy and domesticity, says of Tonga:

never have I seen features so deeply marked with all bestiality and cruelty.

Tonga is the exotic other who threatens to disrupt English life and decency. That the facts of his life don't accord with any particular native group doesn't matter: his existence is largely symbolic of all that is feared in other cultures and ways of life.

His disruptive potential is most potently revealed through his poisonous blowdart gun, which kills Batholomew Sholto and threatens both Holmes and Watson with death. This mysterious, if primitive, weapon represents the ways the exotic "other" can sneak into the English home and wreak havoc. Like an animal—which is the way in which he is usually described—Tonga sneaks into the Victorian domestic environment through small, unexpected spaces, such as a "hole in the roof," representing the potential of surprise attack from the "primitive," who can arrive in ways and forms least expected.

Tonga, and India in general, is a special threat to Mary Morstan, who represents the ideal of Victorian womanhood. Until such exotic threats as black cannibals and Indian treasures stolen from a rajah are removed from her life, she cannot marry Watson and find the safety and normalcy of the English domestic hearth.