How can you figure out the part of speech and
the meaning of the word grievously by breaking
it down to its word parts?

Explanation:

 The word grievously is an adverb , which means very seriously, or in a way that causes great pains . When we break it down to its two parts, we obtain the word grievious (adjective ), which came from the noun grief , and the element that forms adverbs from adjectives: ly  (suffix ), and its meaning is "in the manner denoted by the adjective. The corresponding verb  is grieve.

from the excerpt from the "the dark game" the reader can infer that folke cronholm was spying for the allied nations.