Cryptic crossword No 3,237

It's been a long while, but here's a new one - hope you like it!

Well I don’t know where you’ve been, Alf, but it’s great you came back. This was a lovely puzzle- technically highly accomplished, thematically coherent, stimulating and imaginative- a real work of art! Some special moments: regarding the fall, ends up, craft director, turn of the screw. And pick of the clues: 10a (very clever, just a bit early!), 15a (also superb), 17a, 21a, 1d, 2d, 5d, 14d, & 19d. Feel free to stick around!