Laura Main, 23, said Paul Smith and David Parker arrived at the home she shared with her then partner, Ian Clyde, 24, late in the evening of April 17, 2011.
She said Smith seemed agitated, was unshaven and drunk. The dental nurse told jurors she heard bits of a conversation Smith had with Mr Clyde about a woman being held at a house in West Kilbride, North Ayrshire.
She said: "I thought they were talking about a junkie going cold turkey. They said the woman was agitated at not being allowed out the house." Ms Main did not tell the police about the incident until January 2012 when they were making inquiries about the missing woman, Lynda Spence.
Ms Spence has not been seen since April 2011, and Parker, 38, and Smith, 47, are on trial accused of her murder along with Colin Coats and Philip Wade, both 42.
It is alleged they abducted her and held her at a flat in West Kilbride for up to a fortnight, where prosecutors claim they cut off her thumb and beat her with a hammer and a golf club.
Ms Main said: "If I had known what was happening, I would have gone to the police that night. I ended up in a psychiatric unit because of what it had done to me. It really affected me, because I had kept it to myself."
The court also heard from Alicia Thomson, 23, who said Smith asked her to throw a sim card from a mobile phone into the sea. Ms Thomson said she had been living with Smith since the beginning of April 2011 and the incident occurred in October that year after police left a flyer at their home in Largs regarding Ms Spence's disappearance.
She also told the court she had been threatened by Wade, who held a blade to her neck and told her to "keep your mouth shut".
Dental hygienist Susan Birch, 39, told jurors she saw a woman and a man she knew as Paul Smith on the promenade at Largs. She said the woman was taking something apart that she believed to be a phone, then she threw it into the water.
The trial continues.