When the Thrush Knocks...

"Stand by the grey stone when the thrush knocks, and the setting sun with the last light of Durin's Day will shine upon the key-hole." ... Evening was coming on. Then suddenly when their hope was lowest a red ray of the sun escaped like a finger through a rent in the cloud. A gleam of light came straight through the opening into the bay and fell on the smooth rock-face...

Normal sudoku rules apply.

Begin by filling in the "boat" cells in box 7 with the corresponding digits from the previous puzzle.

An X separates digits that sum to 10.

A black dot separates digits where one is double the other.

As the sun sets in the west, a shaft of light will break through the clouds from one of the marked cells in column 1 to form a straight line in that row, illuminating the key-hole in the cliff wall in column 8. Starting from column 1 and ending in column 8, digits along this shaft of light increase as they move towards the key-hole. The remaining four cloud cells contain odd digits.

The secret door in the mountainside is in column 8, three cells in length and centred on the key-hole, containing digits that sum to 24.