It is the Martyrdom of St Thomas Becket from the 13th century, notice the cubic, veiled, free standing altar. There was a fire in the 20th century in the Church which destroyed alot of painting, there is a watercolour from 1880 showing what was revealed in the 19th century, when the whitewash of the Reformation iconoclasts was removed.
Interesting, that the martyrdom of St Thomas is mixed in with the normal schema of eschatological subjects one might expect on an east nave wall. It is perhaps a century later, and much cruder than the Christ in Majesty at Clayton in the tiny Saxon church there, which is a mile or so further north.
The Clayton wall paintings are incredibly moving, I was staying in the village one weekend and knew nothing about them and wandered into the little unprepossessing church, they are breathtaking.
The photographs don't really do them justice, the colours in both churches are red and yellow clay with a little soot black. The limited palette only seems to add to their beauty. There are one or two other examples of such paintings in the area. It is likely they are all the work of painters from the Cluniac Monastery of Lewes Priory.