Police seized suspected heroin with a street value of £10,000 on Friday morning when they met the NorthLink ferry arriving in Lerwick.
Working with Dogs Against Drugs, the police officers intercepted a 36-year-old man disembarking the ferry who was searched and found to be in possession of suspected heroin.
A 19-year-old woman was also detained and allegedly found to be in possession of the drug.
Police estimate the combined street value at £10,000. Both people remain in police custody and a report is being sent to the procurator fiscal.
Temporary chief inspector Lindsay Tulloch said: “Couriers continue to make attempts to carry illegal drugs for sale in Shetland where a market for drugs remains.
“We are determined to disrupt and stop this and again urge the public to help and report anyone who they believe is involved in using or selling illegal drugs in Shetland. With your help we can act to prevent and remove the abuse of illegal drugs in our community.”