4/4 Tom makes a remarkable discovery at Ely Cathedral and meets the mysterious Mrs Bartholomew
3/4 Hatty reveals the secret of the clock - but what does it mean? With Una Stubbs.
2/4 Tom and Hatty become friends in the night-time world, but there's trouble ahead.
1/4 A boy's stay with his relatives turns from tedium to adventure when the clock strikes 13.