Novel object of obsession by detective beset by ridicule (8)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Novel object of obsession by detective beset by ridicule [BY + DI (=detective, i.e. Detective Inspector] in MOCK (=ridicule, make fun of); the reference is to the 1851 novel by Herman Melville, in which Captain Ahab is obsessed with the whale Moby Dick