It is a Friday night in April 1968 in Chicago. Johnny Ross works with his brother Pete; both are involved with organized crime, and the mob is after Johnny Ross because he siphoned off $2 million of their money. Johnny escapes a mass of gunmen outside his office, then greets Pete in the garage of their office building. The two exchange brotherly greetings and go on their way - Johnny drives past yet another attempt on his life while Pete telephones his higher-up that Johnny escaped.
Saturday afternoon in San Francisco. A man goes to a hotel and asks the desk clerk for a message from Johnny Ross, and is surprised that no message is there. The man takes a cab and has the driver stop by a phone booth, where the man makes a pair of calls, one of them long-distance. At that point, Sgt. Don Delgetti of the SFPD awakens his partner, Detective Lt. Frank Bullitt, at his apartment. Bullitt has been trying to get some sleep after a case that stretched to 5 AM that morning and grumpily chats with his partner.
After showering and getting dressed, Frank Bullitt is driven by Delgetti and another policeman, Sgt. Carl Stanton, to the plush mansion of politician Walter Chalmers, who is entertaining a vast pool of guests at a function. Chalmers tells Frank of a star witness who will testify against the mob - Johnny Ross - and who needs protection through his appearence to testify on Monday morning. Chalmers clearly hopes to use Ross as well as Bullitt to the benefit of his political career, and leaves Frank and his two partners to guard Ross at the Hotel Daniels, a flophouse near an overpassing highway.
Frank, Delgetti, and Stanton meet the man who had inquired about a Johnny Ross letter, and the man is puzzled about Chalmers putting him up in this cheap hotel. After phoning his boss, Captain Samuel Bennett, Frank arranges three shifts to guard Ross, with Delgetti going first, then Stanton, then Bullitt. But at 1 AM the following morning Stanton gets a call from the Hotel Daniels fron