The Leaping Angels. The Guardian Angels, #4

How would you stop a group of teenagers from leaping from a hotel balcony to another? That's Lizzie and Danny's next mission - the group test. With graduate, Alex, they use their persuasion skills, memories and concentration on getting to the hotel where the teenagers are. They lose Alex in a dark tunnel, transporting to the hotel. But with concentration and focus on where they have to be, they get him to find them again.
Then when they do reach the hotel where the boys are, it's to find that their enemy, the Dark Angel, has got there first. For during their memory challenge, it starts to go wrong. The teens leap faster and faster from one balcony to another until one boy falls. With 'what if' scenarios and flashbacks, Danny persuades the leader to stop his gang. But then a rival gang arrives. It's now Lizzie turn to prevent them from doing the same.
With memories of her death and what just happened, she persuades them to leave, but the Enemy pushes one of the boys to fall. Alex flies to the rescue, and using transportation skills on other boys, he makes them land on bushes and hedges on the ground. But both boys are hurt, one of them going into a coma. Two groups saved in one day. They have passed their group test.