In Number the Stars, when Ellen asks Annemarie where she put her necklace, what does Annemarie say in reply? It's a book named Number the Stars.
When Ellen asks Annemarie where she put her necklace, Annemarie replies that she "hid it in a safe place...a very secret place where no one will ever find it". Annemarie promises that she will keep the necklace there for Ellen "until it is safe for (her) to wear it again" (Chapter 7).
The necklace about which the girls are speaking is a thin gold chain with a Star of David on it. The Star of David is symbolic of Ellen's family's Jewish faith. During the occupation of Denmark, Annemarie's family at first takes Ellen in as their own, to hide her from the Nazis. When soldiers burst in one night searching for Jews, Annemarie, realizing that the necklace Ellen has always worn will identify her as Jewish, yanks the chain from her friend's neck when she cannot unhook the tiny clasp, and later puts it in safekeeping for her (Chapter 5).
True to her word, when the war is over and the danger is past, Annemarie retrieves the necklace from where she has hidden it, in the pocket of the yellow dress her sister had worn on the night she had announced her engagement. Her sister had died before she could be married, and the yellow dress had been packed away in a blue trunk which stood in the corner of Annemarie's bedroom. Ellen and her family have been in hiding outside of Denmark, but now they can come home again. When Ellen does return, Annemarie will return her necklace with the Star of David (Chapter 17).