'Prickly heat powder," I said desperately to the driver, pointing at Calvin, my eight-year-old son, who was scratching his arms. "We need to find a pharmacy."
Our summer mini-break at Mom Tri's Villa Royale, a boutique resort set on a hill in Phuket overlooking the Andaman Sea, had started off well enough: we checked into a lovely Thai-style suite and then made for the beach below, only accessible by a flight of steps cut into the steep rock face.
Stopping for a brief minute to rub suncream on, Calvin took off at top speed and dived into the crystal water where he spent the entire day, steadily getting browner. My husband and I stretched out on deck chairs under a huge umbrella and congratulated ourselves on finding the perfect place for a restful weekend - the resort is miles from the city and surrounded by endless, empty stretches of beach.
That night, while watching Thai pop singers prance on TV, Calvin suddenly sat up.
"I feel itchy," he said, pulling off his T-shirt to reveal an angry rash all over his body. He began to scratch himself vigorously.
"It's your own fault, you know," my husband told Calvin, while I hunted for the cold cream. "You refused to sit in the shade."
"What's the point of going to the beach if you're going to worry about the sun?" asked Calvin. "Look at all the cool stuff I found in the sea today." He turned out his pockets and seashells, a tiny crab, a knot of seaweed and two starfish tumbled on to the bed in a shower of sand.
"I'm sleeping on the couch tonight," sniffed my husband when the crab tried to run up his arm.
"You're not being helpful at all," I told him coldly. I dialled housekeeping and asked if they had prickly heat powder.
"Sorry, we don't have any," said the polite lady, "but we can arrange for a car to take you to a pharmacy."
The driver, of course, hadn't been briefed on the nature of our emergency, which is how I ended up gesturing wildly in the resort car park in the middle of the night, while my husband and child stood a little way off, pretending they weren't with me.
Twenty minutes and a reckless downhill drive later, we found a store where we were handed a small tin labelled Snake Prickly Heat Powder (Bt25; Dh3). I looked at it in wonder: I had never once come across it in the seven years we lived in Thailand.
The stuff worked like magic. By the next morning Calvin's rash had disappeared, so he immediately insisted on going back to the beach. "Let's hang around the pool instead," I said, trying to lift his shirt for another look. He fended me off expertly and went to get his bucket and spade. "I'm fine, Mum," he insisted. "But don't forget to put the tin of powdered snake in the beach bag."
Ÿ A beach wing suite at Mom Tri's Villa Royale (www.villaroyalephuket.com; 00 66 7633 3569) costs from 8,850 Thai baht (Dh1,076) per night, including taxes.