Surprised to see no votes for 13D as COD -- so clever once the penny drops (which in my case took an age!). Thanks to Rainman for the pointer to 25A -- I just couldn't parse it at all. It is a bit convoluted, though, especially as the clue within the clue element isn't even a particularly common anagram indicator. There are some terrible surfaces, too (12A, 11A, 9A), alongside several lovely ones (3D, 6D, 19D). So, overall, oddly variable this week IMHO. (Maybe one setter did the acrosses and an other the downs!?)