‘Treacherous’ is the third track on Taylor Swift’s “emotional rollercoaster” album, Red (Taylor’s version). The song describes falling in love as dangerous and erratic, but so tempting that you decide to jump in anyway.

Something that is treacherous is something harmful and possibly deceptive — Taylor uses this word to describe a relationship that might not be the best one for her. The song contains strong sensual undertones and while at no point references directly anything explicitly sexual, some of the lyrics can nonetheless be interpreted as a metaphor for sex. Looking at the song through this lens, it can be seen as Taylor realizing that this relationship is moving extremely fast and might be unhealthy.

There are various rumored subjects of the song including John Mayer and Jake Gyllenhaal. The secret message for “Treacherous” featured in the Red album booklet is “won’t stop ‘til it’s over”, a lyric featured on The Temper Trap song – “Sweet Disposition.”. This song is referenced on “All Too Well” – another song thought to be about Jake.

However, the song is most likely about Harry Styles. Taylor confirmed to USA Today that “Treacherous” and “I Knew You Were Trouble” are about the same person, and hints in “I Knew You Were Trouble” point to Harry being the inspiration.

The biggest hint however lies in the songs hidden clue. The hidden message – “won’t stop ‘til it’s over” – is from the track “Sweet Disposition”. This song also contains the lyrics: "Won’t stop to surrender". Harry had a rendition of this tattooed on his arm in April 2012, around the time he was dating Taylor.

Taylor admitted to mocking Harry on his erroneous tattoo and The Temper Trap even recounted in an interview of a time Taylor ran into them:

She was like “Hey”, you know, “I’m a big fan” blah, blah, blah. And she goes “Ah, it’s my boyfriend’s birthday soon I wanna give him a present – here’s a piece of paper, can you please write down the lyrics to "Sweet Disposition”, sign it, I wanna give it to him. So I had this dilemma in my mind at that point – do I write the wrong lyrics? Do I write the right lyrics? I kept it real, I wrote the right lyrics man… And they broke up soon after.

This seemed to be Harry’s favorite track at the time he dated Taylor (around April 2012) as he tweeted lyrics to the song on multiple occasions.