Mason went on to become an established first team member at FC Groningen. During his time in the Netherlands, Mason was voted in Marco van Basten's dream team for up and coming stars and he attracted the attention of much bigger teams such as Ajax and Feyenoord. Though happy in the Netherlands, coming from a large close knit family, Mason always wanted to get back to the UK and closer to home. When Alex Smith offered him the chance to move to Aberdeen in 1988 for £400,000, Mason and his young family returned to the UK and he joined Aberdeen FC at the same time as Theo Snelders who had arrived at the club from FC Twente as a replacement for Jim Leighton. Mason and Snelders remain good friends to this day.
