Mac and our CSIs track the Compass Killer to Flushing Meadow where Eckhart has been living in the World's Fair "underground home" ruins. The team uses surveillance cameras positioned throughout the city to try and pinpoint Eckhart's location. Stella figures out that the three victims had no real involvement in the shooting spree that killed Eckhart's wife and his delusional schizophrenia made him believe they were the individuals that contributed to his wife's death. Hawkes discovers Eckhart is using solar charts and astronomical instruments to guide him in his killings. December 5th, Eckhart's birthday and the day of his wife's murder, is also the day where a biannual solar event called Manhattanhenge occurs, where the rising or setting sun aligns with the east-west grid of Manhattan streets. When Lindsay pieces together paper fragments found in the "underground home" with the notes left on each victim, another sketch emerges, it's of the Compass Killer's forth victim - Hollis Eckhart himself. He blames himself for his wife's death since he asked her to come by his workplace before they went off to his birthday celebration at Lincoln Center. Today is now Mac knows that is where he will find him and rushes to Lincoln Center to stop Eckhart from completing his final act of revenge on himself.