is to substitute plot for personality . 
(ROOT (S (VP (VBZ is) (S (VP (TO to) (VP (VB substitute) (NP (NN plot)) (PP (IN for) (NP (NN personality))))))) (. .)))
(ROOT (S (VP (VBZ ) (S (VP (TO ) (VP (VB ) (NP (NN )) (PP (IN ) (NP (NN ))))))) (. )))