B787 Relief Captain reported the #10 Spoiler unlocked at top of climb and would not restow. The flight crew returned to the departure airport for an overweight landing.

Narrative

I was acting as the Relief Pilot Captain for the flight. During climb out the Relief Pilot First Officer and I proceeded to start our first rest break for the leg to ZZZZ. We were both in our respective bunks when the Flying Captain called me to inform me that they needed both me and the First Officer to the flight deck as that we have a spoiler problem and that we were returning to ZZZ. We both returned to the flight deck and were informed that the number 10 spoiler had popped up and was causing drag on the aircraft. I was also told that the flying crew had discussed the situation with the company and it was determined that the flight cannot continue on its planned flight to ZZZZ and should return to ZZZ since that was the nearest airport.I immediately asked if we were dumping fuel. I was informed that we were not and that is was not planned to dump fuel and we were going to do an overweight landing. This was determined by the flying crew; and the Company I believe; since it was actually safe to do this and it would take a lot of time to dump fuel and since we had a flight control issue; we needed to land at the nearest safe airport. There was concern that there might be more degradation in the control of the aircraft and we wanted to land as soon as possible. The Relief Pilot First Officer (FO) and; with the help of the flying FO; determined if we had enough runway to safely land the aircraft at ZZZ with our spoiler control issue. It was determined that we did. We also determined that we had the performance to safely go around if needed at our weight since we were landing over weight. We determined that we did have the required performance. Even though we did have the required performance for both landing and a go-around; I suggested to the flying Captain that we should consider dumping fuel to lower our weight as much as possible since it would only make it safer. The flying Captain once again thought it would take too much time and they wanted to land as soon as possible considering our flight control issue. We obtained our clearance from ZZZ Center and proceeded to the intersection and then to ZZZZZ intersection for the ZZZZZ arrival and the ILS to XXL. We briefed the approach and landing; completed all checklist including the overweight landing checklist and made an approach and landing to Runway XXL at ZZZ airport. We then taxied to the gate and parked. During the debrief I mentioned that; although the flying Captain flew a very safe approach and landing considering the weight of the aircraft; I was uncomfortable with the weight we landed at because our Vref and target speeds were very high and very close to flap over-speed and to Vmin. I said that this is why I believed that we should have tried to dump as much fuel as possible while we were waiting for a clearance back to ZZZ as that we could have lowered our weight enough to obtain a lower Vref and Vmin speed for a safer approach and landing. It was agreed by all that this should have been done.