For five months, young protesters in Thailand have been challenging a government backed by the formidable power of the armed forces and the monarchy. For the first time, a mass movement is openly calling for reform of the monarchy, shattering a taboo surrounding the royal institution's near-sacred status. Influenced by last year's protests in Hong Kong, young Thais have used social media and drawn on popular culture to outwit the efforts of the Thai police to shut their movement down. An unpopular government has so far been reluctant to use harsh measures against them. The monarchy has lost much of the reverence it enjoyed under the long reign of King Bhumibol, who died four years ago. His less-popular son, King Vajiralongkorn, has alarmed many Thais by accumulating even more power and living overseas. But he is now back in Thailand, meeting Thai royalists and encouraging them to challenge the student-led protests with demonstrations of loyalty. The stage is set for a dangerous confrontation between these two sides.