Flies in the face of danger, one party's leader: that's final, period (7)
I believe the answer is:
diptera
'flies' is the definition.
(I've seen this before)
'face of danger one party's leader that's final period' is the wordplay.
'face of' suggests taking the first letters.
'one' becomes 'i' (Roman numeral).
'leader' indicates taking the first letters.
'that's final' says to put letters next to each other.
'period' becomes 'tera' (I can't justify this - if you can you should give a lot more credence to this answer).
The initial letter of 'danger' is 'd'.
The initial letter of 'partys' is 'p'.
'd'+'i'+'p'+'tera'='DIPTERA'
'in the' acts as a link.
Can you help me to learn more?
(Other definitions for diptera that I've seen before include "Flighty little types" , "Flies" , "Insects" .)