Complex sentence: Charlie writes Ida a letter, and calls the bank heist off, but Beppo blackmails him by threatening to use some preparatory drawings made by Charlie, threatening to send them to the bank's home office.
Split into simpler sentences: Charlie writes Ida a letter, and calls the bank heist off. However, it does not stay off, as Beppo blackmails Charlie back into the scheme with some preparatory drawings made by Charlie, threatening to send them to the bank's home office.