Borderline is a direct continuation of Sidetracked.

As such, this description includes major spoilers for the first book in the series.

Please check out Sidetracked first before reading Borderline!

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Jayde Palmer's summer is not going the way she hoped.
One month ago, Jayde's "casual summer relationship" with Ice Monroe took a strange turn when he introduced her to the world of immortals, a group of feline shapeshifters typically kept secret from humans. Things only went downhill from there as Jayde noticed more and more cracks in Ice's persona and later met James Reid, a young man with which Ice has some kind of history no one wants to talk about.
Long story short: Ice is not the kindhearted person Jayde believed him to be when they first met. She trusted him even after his actions unsettled her, but he turned on her in the worst way, hurting her and using his legal status as her immortal sponsor against her.
Now, Ice's worst enemy is the only one who can help her.
But, as it turns out, James might need her help more than she needs his.