Holly successfully fought a heroin addiction in 2010, but episodes airing next month will see her tempted back to her old ways as she continues to grieve for the loss of her father John.
Unable to deal with her pain for any longer, Holly gets in touch with an old contact and buys some heroin.
Powles told Soaplife: "[She's after] a fix. She needs the pain to go. She can't cope at all - too much has happened. Alex tells her she's the strong one in the family, and says she needs to do whatever she has to do to get them through it.
"The only thing Holly can think of to numb the pain is heroin. She has no intention of OD'ing. She thinks she'll have one fix and work out what to do next. She takes Alex at his word in completely the wrong way."
Reports have suggested that Cain Dingle (Jeff Hordley) will find Holly slumped unconscious outside the village's garage after she has succumbed to temptation.
Discussing how the rest of the Bartons might react, Powles added: "They wouldn't understand it's her escape. It'll always be an issue for Holly - the heroin ghost."
Powles will be leaving Emmerdale later this year.
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Watch a preview of Wednesday night's (February 29) Emmerdale episode in the video below: