spot

Could you please let me know what 'take the lead in a spot of' means?

A streak of what looked like molten silver hung shining in the wand's wake. Momentarily shapeless, it writhed and then formed itself into a gleaming replica of a human hand, bright as moonlight, which soared downward and fixed itself upon Wormtails bleeding wrist. Wormtail's sobbing stopped abruptly. His breathing harsh and ragged, he raised his head and stared in disbelief at the silver hand, now attached seamlessly to his arm, as though he were wearing a dazzling glove. He flexed the shining fingers, then, trembling, picked up a small twig on the ground and crushed it into powder. "My Lord," he whispered. "Master ... it is beautiful. . . thank you... thank you. ..." He scrambled forward on his knees and kissed the hem of Voldemort's robes. "May your loyalty never waver again, Wormtail," said Voldemort. "No, my Lord . . . never, my Lord . . ." Wormtail stood up and took his place in the circle, staring at his powerful new hand, his face still shining with tears. Voldemort now approached the man on Wormtail's right. "Lucius, my slippery friend," he whispered, halting before him. "I am told that you have not renounced the old ways, though to the world you present a respectable face. You are still ready to take the lead in a spot of Muggle-torture, I believe? Yet you never tried to find me, Lucius. . . . Your exploits at the Quidditch World Cup were fun, I daresay. . . but might not your energies have been better directed toward finding and aiding your master?"