Concealed difficulty in contract? Strike (5)
I believe the answer is:
catch
I believe this is a triple definition!
'concealed difficulty' is the first definition.
(I've seen this before)
'in' is a link.
'contract?' is the second definition.
(to catch an illness is to contract it)
'strike' is the third definition.
(I know that catch is a more specific form of the action surprise)
(Other definitions for catch that I've seen before include "fellow hooked for matrimony?" , "Getting round" , "Book by Joseph Heller" , "Get a grip on" , "problem being concealed" .)