Three Little Lies by Lauren Marshall (Novel)

2005: Teenage friends Ellen and Sasha attend a NYE party that ends in dramatic fashion resulting in a court case in which Ellen is a key witness. 2018: Still best friends, Ellen and Sasha share a flat in London, now 30-year-old adults. When Sasha goes missing, Ellen is forced to confront what happened all those years ago on NYE and uncover the truth about the past-and her best friend.