Translation:Particularly the second book is important.
I just found an answer to that: when the adverb modifies the subject, the verb does not have to change position. Another example where the verb does not change position would be: "Auch ich und meine Frau sind dorthin gegangen." ("auch" refers to the subject "ich und meine Frau".) In a different example, if someone tells you to read a book and "Insbesondere beinhaltet das Buch viele praktische Beispiele.", then "insbesondere" refers to the entire sentence (you can also say it modifies the verb), in which case the verb needs to come to the front.
About the verb not being in the second position, this is what a native said in a similar post:
German focus particles (‘nur’=“only”, ‘sogar’=“even”, ‘auch’=“too”) must immediately precede the focus. So if the focus is at the beginning of the sentence, the verb gets pushed to the third position in a declarative sentence. Move the focus elsewhere, and the verb is in the normal second position, as in ‘Dieses Buch können sogar Kinder lesen.’.
It was most likely "besonders schön" (especially beautiful). "Besondere" is the feminine or plural for "special", as far as I know.
"Besonders" could be used in this sentence, but it would be: Das zweite Buch ist besonders wichtig - The second book is especially important.
I am no expert, though.