How does the author present the shifting power within the group as leadership passes from Blackie to T?
Greene wishes to show power to be a fluid dynamic in the modern setting. It is not fixed. Rather, it changes and its trappings are shown to be both attractive and fundamentally elusive. For Blackie, his need to hold power is something that Trevor casts as part of the "old" vision. Trevor's claims to power is that he wishes to take the gang into a new direction and a new set of conditions that it has never seen. Such an appeal proves to win over the gang, and as Blackie goes along with it in order to maintain his own place in the gang, power is shown as a narcotic- like light. As leadership passes, Blackie shows that he yearns for power that he would not leave the gang, even as it has become evident that he no longer possesses it.
The narcotic of power is what consumes Trevor in his time as the gang's leader. He is overcome with it and this represents how involved he is with the plan of destroying the house. When it becomes clear that Trevor cannot sustain the interest of the other members, power is shown as a complex entity. The same tools that one utilizes to gain power are not always the same that one uses to sustain it. Through this, Trevor loses power and Blackie regains it. Power is shown as a shifting quality, intrinsic to a modern setting where structures have been dismantled in the face of something unclear, but always changing.