The story about a boy who finds friendship through a shared film project and regular cinema visits is set in the 1940s in 'Sternsea' – a fictional location heavily influenced by Portsmouth and Southsea and featuring local cinemas and theatres.
'I use some of the names of real locations in the book and others have been changed slightly. I've kept the name of the Kings Theatre, but Albert Road has become Princes Road,' says the 60-year-old author of children's classic Goodnight Mister Tom.
'Some of these places are very important to me, particularly the Kings. I spent a lot of time there when I was growing up and saw some wonderful productions. They had the most fantastic shows there, with people like Vanessa Redgrave and Sir Kenneth More.
'I think just about every bit of money I had was spent at the Kings Theatre. I only had to walk up the road to it, so it was a bit like a second home.'
A large part of the focus of the 40s-set story is on cinema and Michelle has used a mixture of experience and research.
'It was quite strange, I'd sometimes make things up in my head and find they really happened. I had this thought about a cinema in Portsmouth beginning to show European films and then discovered that the Rex closed down for some sort of refurbishment and opened with the Rossellini film Rome Open City, and then showed one European film after another.'
Michelle was born in 1947 but she has fond memories of Portsmouth cinemas a bit later than the era she has focused on in the book.
'I remember going to the Rex for an overnight showing of War And Peace. We stayed overnight and had breakfast in the morning. I took my younger brother and was really worried that he'd be bored because it had Russian subtitles. He absolutely loved it.'
Michelle now lives in Petersfield but she's delighted to be taking part in this year's Portsmouth Festivities, talking about her work and giving a reading from the new book at the Menhuin Theatre at Portsmouth Central Library on June 27.
'I have a soft spot for festivals because it gives me the opportunity to speak to people of all ages,' she says. 'Adults seem to like the book. Today for instance I had someone in their 60s telling me they were up until 2am reading it. It might be that it's set between 1945 and 1950 and there's a nostalgia factor. But I also think a lot of adults like my books for what they are.'
Just Henry is about a 14-year-old boy influenced by his bigoted grandmother, who goes on to learn a few things through regular cinema visits and a new and unlikely group of friends.
And Michelle hopes all age groups will attend her talks so different generations can learn something too.
'I once read a story set on VE Day to a mixed audience. A lot of people started talking to their grandchildren about things they'd never told them before. Sometimes younger people don't realise or remember what the old have done. They just think of them as people who shuffle around in their slippers all day.'
Michelle seems to have a fondness for period settings. The Guardian Children's Book Award-winning Goodnight Mister Tom, first published in 1983, sees a young boy sent to the country as an evacuee. Willie, badly treated by his disturbed, fanatical mother, begins to flourish in the nurturing care of Tom. In 1998, it was turned into a hugely popular drama starring John Thaw.
Hard-hitting, the book is ultimately optimistic but there are disturbing incidents of child abuse that are a challenge for young readers.
'I think it's being read by some children too early,' says Michelle. 'Just because the character is eight or nine, it doesn't mean it's for that age group. Some of it is very unsettling but those elements are truthful to the character and story and I don't believe in not telling the truth in order to get published. But I thinks it's more suitable for older children, from about 11 or 12. Although some younger children seem to be okay with it.'
Michelle worked for many years as an actress and writing children's books was one of her ambitions. 'But I thought it was something I would achieve at about 80,' she says. 'Instead it happened for me in my 30s.'
She also writes musicals and for the past 19 years has juggled her writing with motherhood. Michelle's oldest son Tom, 19, is studying costume design at college and her youngest, George, 14, learns at home.
'He has had difficulties. The only way I can describe it is a dyslexia of speech. I was having problems getting him into a school and finding him the education he needed. So I decided to home school. It hasn't been easy but the reward is that he's flourishing. He has a high IQ and when his speech is up to scratch he'll fly. He's doing wonderfully already. He has an aptitude for music and he's been writing – dialogue would you believe!'
So the future looks bright for George, and for Michelle who is hoping Just Henry will follow Goodnight Mister Tom on to TV screens.
The book has been optioned by ITV and a scriptwriter is doing a treatment of it. That doesn't mean it will definitely become a series but it does mean ITV are so interested they don't want anyone else getting their hands on it.
And Michelle hopes that if that happens, the setting for the series will also be her home city. 'I read that Portsmouth wants to encourage people to do filming down here, so who knows,' she says. 'I think that would be wonderful. It would be the perfect place.'