At around 2.30am Sunday morning, a 35 year old woman was walking through the car park at Bridge Street, near to Norfolk Street, when she was pulled into bushes near to a bank by a man who seriously sexually assaulted her.
She had been attending a party nearby and was dressed as a bride wearing a full white dress and a veil.
The woman, who also sustained cuts and bruises during the attack, managed to make her way to the road where she stopped a passing taxi.
Two members of the public also came to her aid.
Detective Inspector Liz McLean, who s leading the investigation, said: "Two members of the public, a man and a woman, stopped to help her as did a passing taxi driver, all of whom have been traced and spoken to by officers.
"However, we are still keen to speak to anyone who was in the area at the time who may have information that will help our investigation."
"Although a lot of people were no doubt dressed up for Halloween parties last night, I think it is very possible that someone may have seen her as she walked along the street.
"From CCTV, another couple, a man and woman both wearing fancy dress are seen in the car park at the time of the attack. I would appeal to them to come forward as they might have seen something that could help us with our enquiries.
"This is a busy area with cars and buses and in particular taxis. I would ask that anyone with information contact police."
She also confirmed there would be extra patrols in the area.
The man is described as white, Scottish, with dark hair and wearing dark clothing, and was said to run off towards Eglinton Street after the attack.