Indore: An 18-year-old girl was allegedly raped by a youth on the promise of marriage, on Thursday. Jyoti Sharma, in-charge of women police station, said a case under relevant sections was registered against one Mohammad Rahil, a resident of Kadawghat area.  Both the victim and accused met about 9 months ago and the accused promised her for marriage. The victim alleged that Rahil had raped her when she was alone in her grandmother’s house. Later when the victim asked for marriage, the accused threatened her of dire consequences. Police have started investigation into the case.