Try something like this. This is the way I have it and it matches correctly
The Mentalist.S02E21.18-5-4
I suspect you have something more closely related to this
The Mentalist (2008) - s02e21 - 18-5-4
or
The Mentalist (2008) - s02e21-18-5-4
You may have to Plex dance <-click
