In Rock is one of the most important albums ever recorded, so much so that an entire book has been written about it. In Wait For The Ricochet: The Story of Deep Purple In Rock, authors Simon Robinson and Stephen Clarey say of "Bloodsucker" - Track 2 - it was the final song prepared for the album; written around the beginning of April 1970 towards the end of the sessions. Although a group composition, it was written (primarily) by Messrs Glover and Blackmore away from the rehearsal rooms or the studio. According to the bass player himself (quoted verbatim): "Bloodsucker originally came from a rare evening at Ritchie's flat in Acton, he and I writing together on acoustic guitars. It was later finished with the rest of the band in Abbey Road Studios."