What date (roughly) did you put the link up? Have you cross-referenced that date with Moz's Google Algorithm History http://moz.com/google-algorithm-change#2013? I would first look at your drop in rankings compared to the algorithm updates to see if there is any correlation there. That seems more likely to me.
Also, you could consider running http://www.styleshout.com/ through OSE to see if it has any dubious back links. From my understanding, certain pages can have a high page rank, but still have a dangerous links that could hurt you.