Nervous, twice circling edge of dangerous whirlpool (9)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

CHARY = nervous, BIS = twice, with D the edge of dangerous inserted. Depending on the version of the legend, Charybdis was either a sea monster (opposite Scylla) or the whirlpool created when the monster belched out swallowed water.