The PCs fought a dark elf and a gray slaad. The PCs killed the dark elf, but the gray slaad used plane shift to escape. The PCs found among the dark elf's gear the gray slaad's control gem.
Must a PC attune to the slaad control gem to be able to use it?
Further, after attuning to the control gem if necessary, can the PC use the control gem to cause the slaad to return to the PC's plane, or is the slaad uncontrollable forevermore after it leaves the plane where its control gem resides?