Ghoulia and the Mysterious Visitor by Barbara Cantini

Ghoulia is in for a surprise.  Her aunt has invited her friends and even an unknown cousin to come for a party.  She didn't know about it and her aunt is nowhere to be found.

Amulet Books let me read this book for review (thank you).  It has been published so you can get a copy now.

Her cousin is a bit weird.  He's not happy about anything.  Then one of her friends goes missing.  What's going on? 

While Dilbert isn't the best guest, he turns out to be useful.  While he grumbles at the overgrowing ivy her aunt was cultivating, it starts to recede and die.  And, surprise, she's found her aunt and her friend.

Make sure you know all about a plant before you grow it...

With lots of illustrations and odd characters this is just right for the intermediate readers in your life.