Vial of stench (a) is an inconsumable potion that can be made after the caper A Guild of Our Own. It is created by having Chief Thief Robin in the Thieves' Guild cast a spell on the vial from the caper to activate it a second time. This second activation allows the player to steal from stalls and then immediately sell the stolen goods to the stall owners, as the owners will not be able to identify the player as the thief who stole from them. The vial of stench (a) only needs to be in the inventory for its effect to work.
Players may only have one vial of stench (a) at a time, but it can be remade at any time if it is lost by bringing a vial of stench to Chief Thief Robin and having him activate it.
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