I think I found the movie.

Harlequin is directed by Simon Wincer and tells a tale with echoes in 20th-century Russian history. Nick and Sandra Rast (David Hemmings and Carmen Duncan) have a little boy, Alex (Mark Spain), who is suffering from leukemia.

Like normal parents they will do anything to help their son, especially Sandra. So when Gregory Wolfe (Robert Powell) comes along with his faith-healing techniques to treat Alex, Sandra is particularly impressed. What complicates matters is that Alex's father Nick will soon be running the government and his career depends a lot on Doc Wheelan (Broderick Crawford), his mentor.

Trouble starts when Wheelan cannot abide the faith healer, causing the mysterious Wolfe to react in a most unexpected way.