When Harry the alien lands his spacebin in his friend Colin's garden, it's time for an adventure! There's just one problem - they'll have to take Colin's naughty, snotty little brother with them... Colin's day is about to turn Cosmic! But when aliens attack, will it end in disaster?

Colin wants to go exploring in space some more--will babysitting duties leave him earthbound?

Colin comes back down to Earth with a bang when his parents force him to look after his annoying little brother, David, for the day. To make matters worse, David has a terrible cold and his constant sniffles and sneezes are starting to really annoy Colin. When Harry lands his space bin in Colin's back garden, things start to look up. But Colin has a very difficult decision to make: bring his snotty little germ-ridden brother along on a space adventure or leave him at home--alone.