I'm not sure specifically as there could be many different interpretations of such a fan fiction. It might involve a character named Mary being attacked within the context of the 'In Plain Sight' universe. But without reading it, it's hard to say more precisely.
You could try searching on popular fan fiction websites like Archive of Our Own or FanFiction.net. Just type in the title 'In Plain Sight Mary Attacked' in their search bars.
It's not a true story. 'Taken in Plain Sight' is a work of fiction that might draw inspiration from various elements but doesn't represent real events or people. The plot and characters are fabricated to engage and captivate the audience.
It's hard to say for sure. It might incorporate elements of truth but could also be a completely made-up tale with a similar theme to real-life incidents.