Epidemic? Change will involve steps (10)
I believe the answer is:
pestilence
'epidemic?' is the definition.
(I've seen this before)
'change will involve steps' is the wordplay.
'change will' becomes 'pence' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'involve' means one lot of letters goes inside another.
'steps' becomes 'stile' (I've seen this in another clue).
'pence' placed around 'stile' is 'PESTILENCE'.
Can you help me to learn more?
(Other definitions for pestilence that I've seen before include "it's an agent of evil" , "that'll plague you" , "morally harmful influence" , "Deadly epidemic disease" , "Epidemic disease with a high death rate" .)