be (dead) set on (something)
To have a strong (and sometimes inflexible) desire for something. We were all dead set on traveling to Spain for the summer, until Lizzy broke her leg and we had to cancel it. I wanted to spend the money on a new car, but my husband was set on getting new furniture for the living room.
be dead set on (something)
To be intent on doing or obtaining something. I am dead set on going out today, so a little rain isn't going to stop me. She's dead set on this house, so she'll be heartbroken to hear that her offer's been rejected.
be dead set on something
If you are dead set on doing something or having something, you are determined to do it or get it. I'm dead set on getting dancing lessons now. To my surprise, he was dead set on a new career as a solicitor.