This film, like its predecessor with Ray Milland and Donald Pleasence, focuses considerably on the antagonists—specifically, a delightfully corrupt Bette Davis as "Letha" and Christopher Lee portraying the eccentric scientist "Victor." It's striking how much taller Lee is compared to his shorter acting partner! The two children are sent to Los Angeles for a trip. While entering the city, they get split up; “Tony” (Ike Eisenmann) saves someone he believes has attempted suicide, only to discover it’s “Sickle,” Davis' relative and Lee's test subject for mind control. Tony is then drugged and taken captive as they engage in various escapades while Letha looks for valuables. Simultaneously, "Tia" (Kim Richards) has freed the "Earthquake Gang" from a juvenile version of "West Side Story," and together they begin searching for her brother. The adult actors deliver entertaining performances; the plot includes several unexpected developments involving goats and blackmail, and there are some simple, pleasant special effects used throughout this somewhat predictable fantasy. It's a solid continuation of the series, making it an enjoyable film for families.

Source on TMDB