Just how much did Frank Randall know? That’s been a big question for fans throughout the Outlander books. It’s clear by the ninth book that he knew a lot more than he wanted Claire to know about.
It’s even possible that Frank knew Claire may have been able to time travel from the beginning. He was in MI6 after all. With the amount of spy work and classified documents he would have had access to, there’s a chance that he found out something about time traveler during World War II. As a historian who looked through historical records around the time Claire traveled back to initially, there’s even a chance he’d found her name written down somewhere.
The latter all depends on how time travel works, of course. Diana Gabaldon has shared that time is linear and not a loop. I just can’t see how that works with how Claire is changing history in small ways.
Back to Frank, though. Here’s why we need a series about him.
Outlander has already given Frank more airtime than the books
We got to see what Frank was doing in his own time while Claire was first in the past. We learn that he stuck around in Inverness for six months as he figured out what had happened to his wife. He just realized eventually that he had to move on.
When he learned that time travel was potentially true, he asked that Claire never look up where Jamie was in the past. That didn’t stop him from looking. After all, he would have initially wanted to see if Claire was telling the truth about being in the past. Her name was on the paperwork to sign the deed of Lallybroch over to Young Jamie, and Frank was sure to find that.
The show also made it clear that Frank learned something in the 1960s. Brianna sees him as he is at his desk, and it’s clear that he has learned something that he didn’t like. He made sure Bree knew how to shoot despite him never showing an interest in hunting before. It was like he was preparing her for the past.
In the books, we learn that Frank definitely knew a lot. We need an Outlander spin-off series that focuses on Frank Randall to tell us exactly what he knew and how. Did he take Claire to Inverness in the first place on purpose to see if she could time travel?
Whether fans like Frank as a character or not, there's an interest in him. The show can continue the Outlander universe with a series about him.