Megastar Amitabh Bachchan launched a book titled `Quantum Siege`, penned by Brijesh Singh, additional commissioner of police North Mumbai, here.

`Released a book written by a Police officer of the rank of Asst Commissioner, Brijesh Singh ... from minding to binding !!` tweeted Amitabh Saturday.

Prior to that, he was busy shooting for his cameo role in `Ghoomketu`, which is directed by Pushpendra Mishra and features Nawazuddin Siddiqui as the protagonist.

"That done it is a quick drive of an hour, a change of dress, a hurried drive across to the Marriott and the book release of 'Quantum Siege' written by a police officer, here in Mumbai," he posted on his blog http://srbachchan.tumblr.com.