Read new novel before mind finally strayed (8)
I believe the answer is:
wandered
'strayed' is the definition.
('wander' can be a synonym of 'stray')
'read new novel before mind finally' is the wordplay.
'novel' indicates an anagram.
'before' says to put letters next to each other.
'finally' indicates one should take the final letters.
The last letter of 'mind' is 'd'.
'read'+'new'='readnew'
'readnew' anagrammed gives 'wandere'.
'wandere'+'d'='WANDERED'
(Other definitions for wandered that I've seen before include "Roamed, roved" , "Rambled with no particular destination" , "Move about aimlessly" , "Went roaming" , "Walked aimlessly" .)