Lisbon is Red John. She is an excellent actor and has been manipulating Jane from before he even met her. She is completely in love with Jane and perhaps fell in love with him when she saw him on TV. She uses her position as Jane's closest friend to be close to Jane and strings him along, relishing the time they spend together. To her they are living a happy life together. She thinks that no one knows she is Red John, and Jane suspects her but is conflicted about it as his suspicion grows. 

She has another accomplice or many in the CBI. Rigsby is likely one of them. Lisbon thinks that he doesn't know that she is Red John, but perhaps he suspects she is or even knows. Grace who may or may not  be a disciple of Red John, unaware that her coworkers are accomplices, will be Lisbon's trump card against Rigsby, who like Jane, might also be after her for his own reasons, maybe for revenge or to "become" Red John.

If Rigsby is an accomplice to Red John he will likely kill Cho. Jane will set a trap for Lisbon, but Rigsby or some other accomplice will mess it up. Jane will be "fatally wounded". Lisbon will confess her love to Jane and he will actually die but catch Red John by recording her confession or having it witnessed.