“Don’s Plum” seemed destined for success. But when the film starring Leonardo DiCaprio and Tobey Maguire was blacklisted by its stars, the cast fell apart — and destroyed lives. Find out the dirty details of the lawsuit, and eventual overseas release, in the finale of “The Curse of Don’s Plum.” “This breaks my heart to this day,” filmmaker Dale Wheatley said in an emotional sit-down with The Post. “I was afraid to go to my own premiere.” He skipped the Berlin Film Festival in 2001, fearing legal backlash, and eventually made just $180 for his work. The dark cloud hovering over the film follows him to this day.