After about 15 minutes, Grissom in Houston started calling up to the spacecraft, trying in vain to be heard. The spacecraft was fast approaching the night side of the planet where it would be too dark for White to see. They would also be out of communications range with Houston. Mission control wanted everything squared away before that happened, but Grissom's ten calls in over a minute went unanswered.
Finally, McDivitt decided to check and see if the ground had any pending messages. Flight Director Chris Kraft famously came online and spoke to the crew directly in this one instance: "Flight Director says get back in!"
McDivitt passed the order to White who pleaded for more time "Back in? Aw, Cape, let me just find a few pictures... Listen, you could almost not drag me in, but I'm coming." He made his way slowly to the open hatch using the tether as a guide. "This is the saddest moment of my life," he announced as he starting making his way inside.
The EVA was a success, particularly for NASA's first try. But White had had a basic mission plan - NASA was most interested in gathering data about any disorientation he felt in orbit, ease of maneuvering, and comfort in his EVA suit. Later missions would demand spacewalking astronauts perform more complex tasks. White's spacewalk was an excellent start that taught NASA a lot about EVA dynamics, but the mission also taught the agency that it had a lot more to learn before astronaut would comfortably work in the vacuum of space.