Even the opening title-frame 'One Step Beyond' is botched. It actually appears to read 'Beyond Step One' - ironically a pretty accurate guide to the sort of production values to be expected.
The concept appeared to mirror another hosted anthology series about irrational phenomena, 'The Twilight Zone', along with the dubious plus-point that this one was based on 'human record' - sliding out from actually stating that these were true-life dramas. In the case of the present episode, it would defy belief anyway, partly due to the flimsy plot, and partly to the excruciatingly bad acting.
Our host John Newland tells us we're about to witness an at-home wedding. "The bride will come down these stairs..." (You don't say.) Then the backstory. Groom and Best Man were buddies in the war, which apparently ended a year ago. So we're in 1946 (not strictly a period piece in 1959) and the two of them are taking a final bachelor holiday in the Alps, when the Best Man dies in a fall.
The Groom, a poor man's Leslie Howard, not surprisingly as he is actually the great man's son Ronald, appears to be making the best of things until it comes to light that he had always suspected the other man of having designs on his fiancée, and conveniently arranged the death on the mountain - perhaps the most unlikely thing a groom would want to do to the person who has just agreed to be his Best Man at the wedding of the disputed female. Also he didn't reckon with karma, which comes back with a vengeance, making its (chilling) presence felt all through the wedding ceremony...
The nearest approach to a good performance is by Christine White as the bride, though at 33 perhaps a little too old to carry conviction. The rest are just too hammy for words.