Hello Cliffcrest is a quest given to the player after Harry has woken up from his sleep. He tells the player he knows where Robson has gone into hiding, his small home in Cliffcrest.
Harry reveals he had a vision in his sleep that the girl at town hall Wendy is attracted to men with drugs and will reveal to the player where Robson is if the player offers her drugs. He goes on to say that there is a known drug dealer in town called JC and that he can sell the player drugs if you speak to him.
The overview of the quest is to go and talk to JC who will ask you to do his Get Fragged Nelson sidequest before potentially offerring to sell drugs to the player. Depending on the outcome of this sidequest he will either sell you drugs or you will have to kill him.
If you kill him, use the key you got on the Get Fragged Nelson sidequest to get into Nelsons house. He has drugs. If you dont kill him, you can either buy drugs from JC or loot Nelsons house for the drugs.
Give those to Wendy and she will tell you Robson lives in town at the end of the street next to the ultimate parkour building close to the train station. Head into there and talk to Shirley the parrot who will repeat the last few things Robson said.
Shirley reveals that Robson has hidden in a cave underneath his house. Head into the cave and talk to Robson. He will give the main quest Taylors Revenge I.