Bob penning long chapter that's terrifying (5-8)
I believe the answer is:
spine-chilling
'terrifying' is the definition.
(I've seen this before)
'bob penning long chapter' is the wordplay.
'bob' becomes 'shilling' (I've seen this before).
'penning' indicates putting letters inside.
'long' becomes 'pine' (to pine for someone is to long for them).
'chapter' becomes 'c' (abbreviation).
'pine'+'c'='pinec'
'shilling' placed around 'pinec' is 'SPINE-CHILLING'.
'that's' is the link.
(Other definitions for spine-chilling that I've seen before include "Terrifying" , "Scary" , "Arousing terror" , "Inspiring both terror and excitement" , "Bloodcurdling" .)