JOHANNESBURG, South Africa - Zimbabwe's main opposition leader was involved in a plot to assassinate or overthrow Zimbabwe's President Robert Mugabe, a consulting firm with ties to Mugabe's government claimed Wednesday. An official at Dicksen & Madson said he secretly taped a meeting with Morgan Tsvangirai, president of the opposition Movement for Democratic Change, where they discussed removing Mugabe from power. Tsvangirai was apparently unaware of the firm's connection to the government. The grainy footage was broadcast on Australian television Wednesday night. Tsvangirai told The Associated Press the tape was "contrived." He refused to comment further, but opposition spokesman ...