A juror is poisoned while sitting in the high profile murder trial of Lyla Addison. The victim had been poisoned with cyanide. Castle and Beckett entertain ideas of the juror being involved with the case after finding out he bought his way onto the jury.
The detectives find that the victim had sent evidence to the district attorney providing the defendant's innocence. The DA withheld the evidence because of his campaign for mayor and he needed the backing from the Addison family. Captain Montgomery forces him to hand over the evidence, leading Castle and Beckett to find the defendant to be innocent and the juror died trying to prove it.
Lyla Addison had been killed by her own brother and the victim's brother happened to be a witness. He had passed along the information to the juror.
Castle finds Alexis lying to him, only to find out that her friends had shoplifted and she had gone back to pay for the merchandise.
Beckett and Castle head to the movies after the case is closed.