"He remembered Indian Island as a boy"

'Dances With The Wind In His Hair'
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Although it seems astonishing to today's sensibilities, the original title of the book was Ten Little N_____s. We'll look more at the reasons Christie chose that title when we examine the poem in the Bookmark for page 31. Because the term was quickly considered offensive, her publishers subsequently changed the title to Ten Little Indians. Hence, the name of the island had to be changed as well:

Original text: He remembered N____r Island as a boy. . . . It had got its name from its resemblance to a man's head--a man with negroid lips.

Revised text: He remembered Indian Island as a boy. . . . It had got its name from its resemblance to a man's head--an American Indian profile.

(Source: Sanders and Lovallo, The Agatha Christie Companion [New York: Delacorte Press, 1984], 182)

Interestingly, in the last few years the term "Indian" referring to the indigenous peoples of North America has, in turn, become offensive to some groups. "Native American" is usually the preferred term nowadays. This has resulted in yet another change to the novel--removal of the references to "Indian Island" and "Ten Little Indians" and insertion of "Soldier Island" and "Ten Little Soldiers." It's difficult to imagine that the term "soldier" will ever become offensive.

For a thoughtful discussion of the term "Indian," see this usage note.