The diagnosis of abruptio placentae praecox of the second twin is usually difficult. The clinical symptoms may not be evident. The appearance of the new (third) hypoechogenic space, on ultrasound scan. was in our case the only diagnostic clue. It proved to be blood from the abrupted edge of twin B's placenta penetrating the dividing septum. Its characteristic ultrasound image brought forward the idea and namegiving ‘boomerang phenomenon’ and indeed, it could return like a boomerang as the intrauterine fetal demise, if ignored. This picture could mislead to the conclusion of being the leakage of amniotic hid or the amniotic sack of the' vanishing fetus' in primarily triplet pregnancy. The potentially ominous prognosis of abruptio placentae praecox warrants strict supervision of pregnancies with this phenomenon.