If you were going to do "Just One Thing" to improve your health or wellbeing, what would it be? Science journalist Michael Mosley shares simple tips that could transform your health, with some surprising benefits. In north Wales, busy single mum Jayne is looking to give her energy levels and immune system a boost after a difficult year. She's keen to try and get rid of the coughs and colds and have the stamina to enjoy lots of exciting active challenges with her energetic kids. Michael challenges Jayne and her friends to try a cold shower every day, but will they embrace their chilly challenge and unlock a host of potential benefits?