Many of the ingredients of classic children's stories are here: a missing mother (because who can have an adventure with Mum around to check up?); endearingly mad older relatives; a mystery to solve; friends and less-than-friendly kids at school. Reading this had a nostalgic feel, probably because it is vaguely reminiscent of books I grew up with, although at the same time it is firmly set in the here-and-now with mobile phones and environmental worries.
Nina is a great character: grounded, caring and just trying to get on with things the best way she can. Children will relate to her with ease, and will be cheering her on as she works to unravel the mystery of Mum's disappearance. The aunts are fabulous creations and complement one another beautifully. The real star, of course, is the shop, and this is shown in the chapter headings which are all objects in the shop (many of which you can see around the edges of the gorgeous cover).
The main plot thrust is of course Nina's Mum, but the novel also manages to deal with new school worries, threads about friendship and a lovely sub-plot relating to an upcycling fashion show, as well as an age-appropriate consideration of mental health. There is a real lightness of touch here that makes this a cheering reading experience, even while you're in the middle of it, not knowing where Nina's mother is or how things will turn out.
Overall, I would definitely recommend this book. In the best tradition of children's literature, it raises some difficult questions (e.g. what if Mum just walked out?) and encourages readers to think about less-than-pleasant things, without threatening their security.