u will see in the next chapters but if u want spoilers now...
...
He wanted to revenge Chase, make Grayson apologize, beat him up, bc of all the horrible things Grayson did in the past to his brother. All the help he think he did for chase harmed his brother sonce they're kids. He also lied that chase did it with a dog when he's on rut. Chase has memory lapses bc he doesnt want to release pheromones. It was dangerous for his brain so Grayson lied to make him realize it, to push him to go to pheromone parties.

I was a little bit confused why did Josh wanted to kidnap Grayson ?