Police said the incident occurred at Uttar Poro in Baksha area of Alipurduar district when Liton Chaki has gone for an outing with Angela Biswas yesterday afternoon.
They were supposed to get married in the Bengali month of 'Agrahayan' (November-December).
According to the complaint with the police, when they were riding along a secluded place, a masked man accosted the scooter and demanded money from them and he was given Rs 500.
Not satisfied with the amount, he fired injuring both Chaki and Biswas. While one bullet hit the former in the ribcage, another one struck the woman in the hand.
He suffered severe blood loss during the journey and was later shifted to North Bengal Medical College and Hospital in Siliguri in a serious condition.
No one was arrested as yet in connection with the incident, police said.