‘Zero is the key’ started out really well. The idea of invisible children solving mysteries was great, and Robert J. Guerrera’s ability to explain science for children also is very, very good. But as a middle grade novel not only read to learn something from but also to entertain and to relate to, I missed too much, and I can’t give more than 2 stars out of 5, compared to all the other really great mystery-series out there on the shelves.

by Peter


‘Zero is the key’


Robert J. Guerrera



Reading Level:

Advanced Beginner


December 10th 2014

Publisher, this copy:


Feelings Thermometer:

Declan and Dalya are a couple of very clever 8th grade children – and twins – living in California. They have their own laboratory in the basement of the family house where they invent stuff and make all kinds of scientific experiments. One day, by mistake, after discovering a peculiar sinkhole, they learn how they can get invisible. They don’t exactly know how, but they invent a mechanism so that they can control it, and they decide to keep it a secret.

But when they arrive in Paris on a Europe tour with their mother and father, hell breaks loose in the Eiffel Tower. Someone – and not only one group of people, but two – already know about their little secret and try to get hold of it at any cost.

A teacher with passion for science and mysteries

Robert J. Guerrera’s middle grade novel ‘Zero is the key’ is all about mysteries. Besides from being a part time author, Robert J. teaches English, history and geography at private schools. And it really shows in this novel. It’s packed with definitions from biology, physics and chemistry, and it’s easy to see that Robert J. has a great talent explaining complicated science in a uncomplicated way. Declan and Dalya also travel world solving mysteries (I gave up counting after visiting five places), so that’s where Robert J.’s passion for geography shines through.

I was very hooked in the first chapters. Declan and Dalya were likable, and I also liked the idea that not all children are at the same level as their grade in school. A lot of clever kids are several years ahead. And nowadays where clever children sometimes are bullied – just because they are clever – it was a great thing to see Robert J. taking their side.

The story wasn’t a slow starter either. The twins discover the ability of being invisible right away, and that made me really excited because it could be used in so many fascinating ways, and I already looked forward to reading about it.

It didn’t take long time either, before we were in a very action-packed scene in the Eiffel Tower. It wasn’t as good described as when Robert Muchamore creates an action scene in the Cherub series, but it was okay.

Excerpt from ‘Zero is the key’

He and Dalya wanted nothing more than to finish eating and to retreat to the basement. Decland cautiously glanced at Dalya and realized she was terrifyingly aware of his metamorphosis.
‘Trouble’, he thought. ‘My parents are going to freak out if they notice this.’
“Finished! I’m going to my room now. See you later.”
Declan jumped out of his chair and bolted upstairs to his bedroom. Confused, Mom and Dad stared at Decland as he exited the dining room. The rest of the family finished luch and cleaned the dishes. Mom had a special Saturday seminar to teach Latin linguistics at the local university. She had only been a professor at the school for three years when she was promoted to lead the Ancient Languages Department. They all said their goodbyes as Mom darted out of the house to get to the university on time. Soon after, Dad left the house to check on his workers’ progress at a large construction site. The twins decided to go out into the neighborhood to try their new invention outside the lab.
A black unmarked car wound its way around the sleepy suburb where the twins were experimenting with their gizmos.
“Invisible!” commanded each sibling.
The gizmos dutifully responded and concealed the twins from the rest of the world.

Something very important is missing

It was a pretty decent beginning, but after a short while I really missed several important elements there has to be in a good story. For starters Declan and Dalya didn’t seem to be whole persons. Let me explain it with an example.

I’m fascinated by mysteries too. Take an old classic, Enid Blyton’s children in ‘The famous Five’ series, they solve quite a few exciting mysteries. And if we also should take something modern, Roger Muchamore’s young teenage Cherub spies – already mentioned – they are truly fascinating and clever – like Declan and Dalya – when they solve their tasks and mysteries. But as persons, all the characters in ‘Famous Five’ and ‘Cherub’ have very important personal traits in common: They are all very unique, they are all very different and they all struggle with a lot of emotions. The mysteries could be solved easily, but they never are, because the protagonists feelings cause loads of problems.

The great differences between the boys and the girls

In ‘Famous Five’, Anne is the little, fragile child – but also the brave one – whom her big brothers take responsibility for and looks after. And tomboy George (Georgina) goes her own ways and runs easily into conflicts. The same does James in Cherub. He knows he has to act like a professional spy and should put his own feelings behind, but he’s marked by his childhood and he has a violent temper he can’t control, so he has to suffer when he’s sentenced with painful punishments like running in the rain for hours while the other Cherub spies enjoys themselves in the warm cafeteria. Also the great difference between the boys tempers and the girls charming but also scheming way of sticking together, creates really dynamic relationships in the books. All their differences make the stories so much more realistic and credible.

A kind of child robots only programmed for solving mysteries

Of course, I didn’t expect relationships in ‘Zero is the key’ because it’s middle grade, but I really expected to get to know Declan and Dalya as whole persons and as siblings. Even scientists and professional researchers – and maybe in particular those – have peculiar habits and different moods, but Declan and Dalya are just the same throughout the whole book. After the first chapters the story felt like the teachers kind of a perfect field trip: All facts, history, geography and science, but no fun, food or feelings.

They children didn’t have bad or funny habits, they weren’t moody, they weren’t really thrilled either, they didn’t play, they didn’t eat delicious dinners or ice cream in the countries they visited, they didn’t show emotions towards their parents, and I don’t even remember their looks or their clothes described at all. Actually, they were like a kind of child robots only programmed for solving mysteries all day long, every day and every evening too. And that felt really peculiar and really lonely, too, while reading.

Invulnerable like BOLT, the super dog

The story is quite action-packed, and even though that is a positive thing, I didn’t get really excited, because I didn’t believe that anything was at stake. Nothing could really hurt Delan og Dalya physical, and when they didn’t show feelings at all, for example wasn’t scared at any time, well, nothing couldn’t really give them a trauma either. The twins felt invulnerable. It’s completely like in Disney’s animation ‘BOLT’. When the super dog BOLT is invulnerable, his tv-series is just the same, over and over, but the day the scheming cat, Mittens, show him he hasn’t any super powers at all and the he is really vulnerable, the fun begins and you can finally relate to BOLT. Unfortunately, I never got that far with Dalya and Declan because they never stopped being super mystery solvers 24/7.

Too stressed with all the global trips

Declan and Dalya visits a lot of places around the world, and of course I understand that Robert J. wants to pass on his own fascination of these places to the readers, but to be honest, it got too stressed and superficial to me. Less is – absolutely – more. I would rather have read the story where the twins only solved one big mystery in for example Paris, where they begin their Europe tour, if we also could have heard just a tiny bit about the French culture, could have had some descriptions of the cafés, the alleys, the food, the Frenchmen and hopefully some funny – maybe even unexpected – episodes with the twins. They are too serious. They don’t joke, they don’t laugh and they solve almost every mystery (except the major mystery) in just 2-3 pages (you don’t even get a chance to guess yourself). It’s just too easy for them, and they never make any ugly mistakes that leads them astray. I still know it’s middle grade, but middle graders can hold excitement much longer. They are not small children, you have to solve everything for in like 2 minutes.

It should have been Declan and Dalya running the show

The longer I got into the story, the more my frustration grew. It felt more and more like a ride in a Universal Studios Theme Park. It’s really action-packed and with loads of effects, and everything is presented for you in that exact moment your ride passes by. But when you think about it, Declan and Dalya don’t do much more than solve the mysteries perfectly and travel from place to place. Everything else is “planned for them” by the grown up characters. They ask Declan and Dalya the right questions at the right time and delivers the right clues to them. It’s really important when you write a story, that you give the young protagonists their own life. And many authors tell that they often have to change the plot along the way, because the protagonists personality wouldn’t go the ways the author plotted. Then you know, you’re on the right track with your story. It should have been Declan and Dalya running the show, not the grown ups pushing them around to the right clues and the right answers.


I really like the idea of a couple of clever researching twins solving mysteries around the world in ‘Zero is the key’. And I think it’s a marvelous idea for a teacher to use all his knowledge in fantasy books, because stories often gets better when the author has been to the places himself. But apart from the invisibility the idea isn’t actually new, and I really missed so much in this novel.

More important than correct information about places and science definitions is that you as a reader have a warm hand to hold, when you’re going on an exciting adventure, a realistic protagonist with feelings, humour, peculiar and bad habits, so we can relate to him or her. The aspect with the extraordinary scientific interested and very clever children I liked so much in the beginning, also became the major problem in the story, because the children never became more than that, and when I think about it, there wasn’t even one person in the story I felt something for. I just felt numb while the children continued solving new mysteries in new places on the globe.

Actually the cover with the Maya temple says it all. It’s fascinating historic facts, but it isn’t inspiring to grab a novel with a Maya temple that just seems like it has been put through an old Photoshop effect. It actually looks like a textbook from school, but to target the middle graders it should of course have been a drawing of one of the exciting scenes, for example where Dalya and Declan fights the crooks in the Eiffel Tower. With lots of emotions and facial expressions. Also, so you could see what the children looks like.

Finally, it has nothing to do with the novel itself, but now I’m mentioning the cover, it just isn’t the same great feeling reading and owning one of those self-published novels, with the lack of quality compared to the books you see on the shelves in book shops. The blurb on the backside was blurry and hard to read, and the cover generally looked like it has been printed on a cheap printer. ‘Don’t judge a book by its cover’ someone would say! Well, everyone does. Of course they do. A book is a whole packet, and that packet should definitely be tempting. Just take a look at all the posts at #bookstagram at Instagram. The cover does matter for the young readers. Sometimes even more than the novel itself, that’s why the readers have defined the concept ‘a cover-buy’.

Thank you so much for the ARC, I received in exchange for an honest review.