Within the interior, the most interesting historical features are the 14th-century font and 15th-century screen. There is also a nicely carved 15th-century piscina, and an Elizabethan memorial brass. The overall decoration, however, is distinctly Victorian, the result of extensive restoration by Arthur Blomfield from 1869-1871.
There is also a vividly coloured west window in the tower featuring glass by the Kempe studio, who supplied so many churches with glass in the mid to late Victorian period.
St Denys' is a bit awkward to find. If you are coming down the B1043 from the direction of St Neots, turn right opposite a row of thatched cottages. This will take you onto a private drive, from whence you turn right, over a large tree stump, and onto a narrow track between a pair of buildings. This will take you to the church.