Her debut novel, Promise Not to Tell, was published by Harper Paperbacks (an imprint of HarperCollins) in April 2007. Promise Not to Tell was described by Publishers Weekly as "Part mystery-thriller and part ghost story".[1] It was released in Germany by Rowohlt Verlag, under the title Das Mädchen im Wald (The Girl in the Woods), in October 2007. Orion Publishing Group published Promise Not to Tell in the United Kingdom in 2008. A French edition and Italian edition have also been released.
Her follow-up suspense novel, Island of Lost Girls was published by Harper Paperbacks in April 2008. It was a New York Times Bestseller. It was released in Germany by Rowohlt Verlag, under the title Die Insel der verlorenen Kinder (The Island of Lost Children); and in the Netherlands by De Boekerij under the title Het eiland van de verdwenen meisjes (The Island of Missing Girls). Sphere, an imprint of Little, Brown, published it in the United Kingdom in September 2009.
Her next book from HarperCollins, Dismantled, was published in hardcover in June 2009. It was nominated for a Lambda Literary Award. Dismantled has also been released in the UK (under the title Girl in the Woods), Germany, and the Netherlands.
In May, 2011, McMahon's suspense novel, Don't Breathe a Word, was published, again by HarperCollins.
