anchor: Yes, he continued, staring at me thoughtfully, "you will be invaluable." This was naturally gratifying, but Poirot's next words were not so welcome. 
positive: Poirot told me I would be invaluable to the investigation, but in the next breath seemed to disavow my usefulness.
negative: Poirot dismissed my usefulness out of hand and said there was no need for me to be there.