Looking over the grid we can see that block 6 requires a 2 and since column 8 and row 6 already contain a 2, we can eliminate all the cells in the block except the one in the upper right-hand corner, so enter a 2 there.

Now column 9 is missing the 3, 4, 6 and 9. There is already a 9 in block 9 so the 9 must go in the bottom-right cell of block 6.

Looking at the bottom cell of column 9, we can eliminate the 3 and 4 as they both appear in row 9, so the 6 must go there. Placing that 6 eliminates all but one cell for the 6 in block 8. Now there's only one cell for the 6 in column 3 and that eliminates all but one cell in block 4 for the 6 (check the columns, rows and blocks). We can also determine that there is only one cell available for the 2 in column 3.

Now column 3 is missing only a 9 and placing that 9 eliminates all but one cell for the 9 in block 8. Row 4 is now missing only the 3 and 9 and there is already a 9 in block 6 so it must go in block 4 and the 3 in block 6. So the final cell in block 6 must be a 6.

Now let's consider the top-left cell in block 7. By a process of elimination we can dismiss every number except 3 for this cell. (Remember, the 1 and 2 must go in the bottom row.)

Entering the 3 in block 7 now allows us to complete block 9. We can enter the 3 and 4 in block 9 and now columns 7, 8 and 9 are complete. Things will unfold quickly from here on in. Next page>