Unseen by most of the world, the once tranquil port of Aden is being steadily infiltrated by jihadists from both al-Qaeda in the Arabian Peninsular (AQAP) and the so-called Islamic State (IS). They are not in charge of the city, the military forces of the UAE are. But in the last few days disturbing reports have emerged of the summary executions of prisoners by the jihadists, along with their black flags hoisted onto public buildings.