[@PatientBean] I would say make a roll for the initial encounter; preferably either Act Under Pressure—up until he morphed and sped off, he was still walking, so you could've followed close behind—or Read a Bad Situation, because you likely might've noticed his transformation and the fact that he isn't as human as he looked.

I leave whether or not Alexander noticed Tiffany up to Alexander's discretion, but if Tiffany is trying to not be discovered, that might make the roll fall more into Act Under Pressure.