A crime gang spent more than £50,000 seeking clients for young prostitutes trafficked illegally into Northern Ireland, a court has heard.
It ran brothels in Aberdeen, Edinburgh, Cardiff, Glasgow and Belfast and trafficked people from other countries.
Prostitutes and transsexuals were brought to Belfast and there was a travel budget exceeding £60,000, police told Belfast Magistrates' Court.
"Hot A-level students 18-plus" in Belfast were among those advertised in a national newspaper.
Two women and two men have appeared in court accused of crimes related to the operation.
A detective inspector said £54,000 was spent advertising the vulnerable women for sex.
The operation was discovered by police in Belfast who raided a flat at King's Square in the east of the city in July and rescued two prostitutes. Detectives have at least two witnesses to the prostitution.
Yvonne Dawson, 22, from Glasgow, is charged with controlling prostitution from April to July this year, but not trafficking.
Malcolm McNeill, 46, from Hamilton, Lanarkshire; Ashleigh Beuken, 21, of Argyle Street, Glasgow and Stephen Craig, 33, from Albert Road, Clydebank, are all charged with controlling prostitution, trafficking within the UK, converting criminal property and managing a brothel.
All four accused were remanded in custody by Deputy District Judge Mateer.