A lot of money perhaps leads to embezzlement — special investigator now joins fray (5,2)

'joins fray' is the definition.
(to wade into something is to become involved in it)

'a lot of money perhaps leads to embezzlement special investigator now' is the wordplay.
'a lot of money perhaps' becomes 'wad' (wad of banknotes).
'leads to' says to take the initial letters.
The initial letters of 'embezzlement special investigator now' is 'esin'.
'wad'+'esin'='WADES IN'