When you find a wizard spell of 1st level or higher, you can add it to your spellbook if it is of a spell level you can prepare and if you can spare the time to decipher and copy it. Copying that spell into your spellbook involves reproducing the basic form of the spell, then deciphering the unique system of notation used by the wizard who wrote it. You must practice the spell until you understand the sounds or gestures required, then transcribe it into your spellbook using your own notation. For each level of the spell, the process takes 2 hours and costs 50 gp. The cost represents material components you expend as you experiment with the spell to master it, as well as the fine inks you need to record it. Once you have spent this time and money, you can prepare the spell just like your other spells. This spellbook contains the following spells:

1st level: absorb elements, comprehend languages, identify, mage armor, magic missile, protection from evil and good, shield

2nd level: arcane lock, hold person, locate object, misty step

3rd level: counterspell, dispel magic, fireball, nondetection

4th level: banishment, greater invisibility, polymorph

5th level: wall of stone

Kasimir Velikov's spellbook mostly contains spells belonging to the abjuration school of magic. Hundreds of years ago, Kasimir failed to protect his people from Strahd and his conquering army. Since then, Kasimir has penitently committed himself to studying this field of magic. In some small way, maybe he can still redeem himself in the eyes of his people...