### Clue: In the light, dealer's ultimate object of quest! (6)
### Answer: RARITY 
 ### Explanation: Definition: object of quest
 RAY(a beam of light) **containing**(In the …) [**last letter of**(…'s ultimate) "dealer" + IT(pronoun for an object/thing)].
Defn:  As above, with "object" doing double duty;**
or, if you object to "object" doing double duty:
Defn:  The whole clue with "it"=object of quest.