A case that will really interest you (4)
I believe the answer is:
grip
This might be a double definition.
'a case that will really' is the first definition.
'grip' can be an answer for 'a case' (grip is a kind of case). I'm not sure about the remainder of the definition.
'interest you' is the second definition.
'grip' can be an answer for 'interest' (gripping is a kind of interesting). I am not sure about the 'you' bit.
Can you help me to learn more?
(Other definitions for grip that I've seen before include "Clasp" , "Grasp securely" , "Hold fast" , "Engage" , "item of baggage" .)