Possible Clues:

• What trespasser does skinning tench and other freshwater fish
• Go too far for criminal chancer over nothing
• Advance gradually into another's area
• Go past a normal limit
• Impinge
• Chance or potential in Fringe, in a similar way
• Chance or potential in Fringe?
• Intrude, initially encountering natural resistance in bus
• Intrude, seeing heartless Etonian (cold fish)
• Gradually intrude (upon)