If you find someone lying on the floor, in my opinion, you go to see if you can help them. They may have a pulse. May need resuscitation. May need to be put in the recovery position while you investigate. It's also possible, since this tale is set in a rest stop cafe on a road, that there is a gas leak or faulty appliance spewing CO and others would be harmed.
Our intrepid sleuth looks over the counter, sees someone on the floor and says oh, he's dead, though there are no visible wounds or weapons, and starts asking people questions about where they were and what they saw. Nobody else wants to administer first aid either.
Some social conscience is present and the writing is nice and light, which stops me from giving one star. Take a first aid course. Start by assuming you can help.
I read an e-ARC. This is an unbiased review.