Legal highs were stolen during the robbery of a shop in Chesterfield.
A man carrying a bread knife held up Reefers on Knifesmithgate in Chesterfield town centre.
He struck at 3.15pm on Friday, May 30 after walking into the shop with a scarf across his face in a bid to conceal his identity.
Police said the scarf slipped down while he was inside the shop and he was later described as being white, 5ft 3ins tall and of a slim build.
He met up with a taller man outside the shop, who was wearing a grey tracksuit with the hood pulled up.
They both ran off up an alleyway opposite the shop in the direction of the Donut Roundabout.
A Derbyshire Police spokesman said: “A man went into the shop and demanded money.
“He left the shop with cash and some bags of psychoactive substances, also known as ‘legal highs’.”
Call Derbyshire Police on 101 or Crimestoppers on 0800 555111.