In this episode, Alvin, deeply disturbed by Tamara's involvement with Dennis and unable to understand if there is really something between his big sister and the creepy nerd boy or if she is just using... Dennis to fire up Alvin's temper, finally confronts her about it directly and is at least relieved to hear that nothing sexual took place between the two - although this is about as much as he is going to learn. After giving some useful life advice to Amy and mending his relationship with Rachel a bit more, Alvin returns home early for a pleasant surprise in the bathroom...