The most interesting historic feature is the tomb of Sir Nicholas de Carew (d. 1311), who built the imposing castle that bears his family name.
Carew's tomb is in the chancel, opposite a small effigy of an unknown woman on what is either a child's tomb or perhaps a heart burial. In the north transept, otherwise known as the Carew Aisle, is the Jacobean memorial to Sir John and Elizabeth Carew.
In the churchyard is a 14th century charnel house (used for storing bones) probably built at the same time as the church itself. There is a chapel over the charnel house. The structure was converted for use as a school in the 17th century. One wonders how the children felt taking classes in a charnel house
Note that the church is sometimes referred to as St John the Baptist. The alternative dedication to St Mary is much more common.