Simplify the following text for a Grade 5 native English-speaking person.
Original: His belief in the paranormal springs from long experience , which began with the abduction of his sister , Samantha Mulder , by extraterrestrials when Mulder was 12 . His sister 's abduction is a driving force in Mulder 's career throughout most of the series .
Simplified: There is a plot in the show about Mulder 's sister , Samantha Mulder .