Dr David Lalloo diagnoses a returning traveller with a suspected scorpion sting. This episode also follows the work of Dr Lalloo in Africa and confronts a parasitic infection which causes abnormal swelling to the victims’ legs. Dr Bertie Squire investigates another parasite which is lurking in the gut of a young woman. The parasite proves resistant to treatment. A woman returns from a holiday on Madeira and is struck down with a knock-out fever with a challenging prognosis.