Even though she is surrounded by police, the woman does not seem particularly bothered at first.
Only when her belongings, carefully examined by police and a drug detection dog, start going from her pink handbag into plastic evidence bags does she starts to get agitated.
It's Thursday evening in the city ahead of a double long weekend and WA Police have picked Perth Underground to make an early statement for their four-day crackdown on alcohol-fuelled violence.
"Police have been everywhere today," one woman says.
"Even climbing up to the balconies on Forrest Chase, there are heaps of them."
As officers continue to detain the woman and a teenager with her, another group of teens comes down the escalator from Murray Street mall.
Spotting police, they pick up their pace towards the entry gates, only to catch the eye of the sergeant detaining the woman and teenager across the entrance hall.
Another dog team moves to intercept them and the teens quickly assume the position, removing their baggy jackets and skate shoes as the labrador gives them the once over.
It's a productive few hours for the dogs - 12 charges, one arrest and several juveniles cautioned for cannabis possession.
Further down Murray Street, police aren't far away when a man starts an argument with security outside Carnegies.
The sight of handcuffs and five police officers brings him to his senses and he wanders off, his high-visibility jacket disappearing down a side street.
It's a different look across in Northbridge, with fluffy bunny ears and short shorts the look for early Easter partying. Punters trickle in throughout the night, but police are even more visible in the mid-evening lull. "This isn't your typical nightclub crowd in here tonight," one officer says. "Good Friday is certainly a big factor, who wants to come into the city at 10 only for all the pubs to shut at midnight?"
But by 11.30pm the signs are there that some have kicked on a bit too long. An ambulance pulls in outside Metropolis, where a young woman has collapsed on the footpath.
While paramedics help her, a man lies propped against a nearby fence, vomiting into a sick bag.
Even the fortifying effects of a kebab aren't foolproof, with one woman passed out at a table on James Street.
Then its midnight, closing time, and the mood suddenly changes.
There's a sense of aggression in the air, with many people carrying themselves as though they're expecting a fight and others staggering towards taxi ranks.
On Aberdeen Street, two mounted officers negotiate with a drunk, waving away smokers who are blowing cigarette smoke into the animals' faces.
"I don't want to give you the $250 fine if I don't have to, but you are getting a move-on notice," one officer says.
Boxed in by the two huge Clydesdales, the man decides not to argue the point and makes a quick exit.
Police will be out in force tonight and tomorrow night, with Operation Unite set to finish on Monday night.