In the 15th century the south aisle was added with its piers and arches of local granite. The wagon roof dates from this period and also the porch and tower, in Perpendicular style. The tower is of three stages, 54 feet in height, and dominates the landscape over a large area. It is surmounted by an embattled parapet and crocketed pinnacles, the crockets representing dolphins' heads. There is a curious stone cat's head on the south-facing exterior of the tower. The peal of six bells is still rung regularly.
There is possible evidence of a rood screen where the pillars at the chancel steps appear to have been cut to receive one: the parclose screen round the Hengar chapel may have formed part of it. There is a piscina at the east end of the south wall.
Some fine 15th century bench ends are displayed attached to the outside of the front pews and at the back of the choir stalls. Note the "Judas" bench end in the chancel, incorporated in the priest's stall in the choir: it depicts Judas with a money-bag round his neck and the thirty pieces of silver.