The 3rd letter of the answer for 25d doesn't feature in any of the across answers you mention, but three of them feature the 2nd, 4th and 5th letters - just leave a row free for that missing letter (the 3rd sentence of the preamble explains why).
An earlier post (#97) gives information regarding the first and last rows in the grid, and this, together with 29a, should help you position 25d correctly.