Suspect one has come across Greek letter, fifth in total – here? (7)

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

Anagram of ( Suspect ) ONE containing ( has come across ) [ PSI(the 23rd letter of the Greek alphabet) + 5th letter of ( fifth in ) “ total ” ]. Defn: The fifth (out of a total of 24) letter in the Greek alphabet.