Arguably the strongest, or at least most intriguing, premises of the first five films. Unfortunately, the execution of said plot isn't good.
'Hart to Hart: Secrets of the Hart' also features one of the more noteworthy cast lists, as least to me. You obviously have Robert Wagner and Stefanie Powers doing their thing well in the lead roles, but there are also appearances from Jason Bateman and Wendie Malick.
I like the idea behind the plot, but the way it is brought to life onscreen is very underwhelming - borderline boring, in fact. What is given is alright, neither positive or negative, but it could've/should've been a much more enjoyable story to see unfold.
This fifth made-for-television 'Hart to Hart' film marks the exit of regular Lionel Stander, who passed away a few months before this was released. I'm sure his peak came in the television series, but he made for a pleasant side character in the films.
There's also quite the unexpected cameo towards the end - I didn't see it coming!