These are some of the themes and reoccurring events that run through-out the series:

Mysteries, drama, adventure, romance

Gospel message

Healing, salvation, miracles, and dreams

Historical figures, events and places

Plane crashes and museums

Sword-fights, gun-battles, and terrorists

Demons, angels, and zombies

Father / daughter relationships and issues

Music: 

Eighty's hits, and Christian songs

Time loops and time travel (season 2 only)