No ordinary raconteur's floundering over start of story — here's where things go downhill fast (6,3)

'here's where things go downhill fast' is the definition.
(Cresta Run is a ski slope in Switzerland)

'no ordinary raconteur's floundering' is the wordplay.
'no' indicates named letters should be taken away.
'ordinary' becomes 'O' (abbreviation eg in O-Level, Ordinary Level).
'floundering' is an anagram indicator (letters flounder or move around).
'raconteurs' with 'o' taken out is 'racnteurs'.
'racnteurs' anagrammed gives 'CRESTA RUN'.

'over start of story' is the link.
This may not be right. Some or all of it may be part of another bit of the clue.

Can you help me to learn more?