The usual wash-up for the perplexed and mystified:
ACROSS
1A1AA bit of leg shown by skirt's hem (raised) (5)[-----]. last letter from "skirt" = T + raised = HIGH. 4A4ADirty Den's downfall? (3)[---]. anag. DEN. 6A6AOne entering into diplomatic relations is silent (5)[-----]. insertion of one = I into diplomatic relations = TACT. 7A7AHairpiece showing strength and determination? Not half! (3)[---]. delete half of: showing strength and determination = RUGGED. 8A8ALip pulled back with the beginnings of laughter? (5) [-----]. reversal of lip = RIM + first two letters of "the".
DOWN
1D1DFinger tuber, coming up with symbolic object (5)[-----]. finger (e.g. of whisky, etc) = TOT, + reversal of tuber = ME. 2D2DRun up, like a dog's dinner? (5)[-----]. a dog's dinner may very well end up IN CUR. 3D3DPlot hole? (5)[-----]. double def. 4D4DShell-like openings to explore and rediscover (3) [---]. first letters from "explore and rediscover". 5D5D...Not a whole finger, you understand? (3)[---]. partial, from finger = DIGIT.