diff --git a/sync/src/light_sync/mod.rs b/sync/src/light_sync/mod.rs
index 12bb6a11e..bd62b4c70 100644
--- a/sync/src/light_sync/mod.rs
+++ b/sync/src/light_sync/mod.rs
@@ -38,8 +38,9 @@ use light::net::{
 use light::request;
 use network::PeerId;
 use util::{Bytes, U256, H256, Mutex, RwLock};
+use rand::{Rng, OsRng};
 
-use self::sync_round::{SyncRound, ResponseContext};
+use self::sync_round::{AbortReason, SyncRound, ResponseContext};
 
 mod response;
 mod sync_round;
@@ -65,10 +66,10 @@ impl Peer {
 	}
 }
 
-// Search for a common ancestor.
+// Search for a common ancestor with the best chain.
 struct AncestorSearch {
 	last_batched: u64,
-	req_id: ReqId,
+	req_id: Option<ReqId>,
 }
 
 // synchronization state machine.
@@ -101,6 +102,7 @@ pub struct LightSync<L: LightChainClient> {
 	best_seen: Mutex<Option<(H256, U256)>>, // best seen block on the network.
 	peers: RwLock<HashMap<PeerId, Mutex<Peer>>>, // peers which are relevant to synchronization.
 	client: Arc<L>,
+	rng: OsRng,
 	state: Mutex<SyncState>,
 }
 
@@ -240,10 +242,76 @@ impl<L: LightChainClient> Handler for LightSync<L> {
 
 // private helpers
 impl<L: LightChainClient> LightSync<L> {
-	fn maintain_sync(&self, ctx: &BasicContext) {
-		const DRAIN_AMOUNT: usize = 256;
+	// Begins a search for the common ancestor and our best block.
+	// does not lock state, instead has a mutable reference to it passed.
+	fn begin_search(&self, _state: &mut SyncState) {
+		self.client.clear_queue();
 
-		unimplemented!()
+		unimplemented!();
+	}
+
+	fn maintain_sync(&self, ctx: &BasicContext) {
+		const DRAIN_AMOUNT: usize = 128;
+
+		let mut state = self.state.lock();
+
+		// drain any pending blocks into the queue.
+		{
+			let mut sink = Vec::with_capacity(DRAIN_AMOUNT);
+
+			'a:
+			loop {
+				let queue_info = self.client.queue_info();
+				if queue_info.is_full() { break }
+
+				*state = match mem::replace(&mut *state, SyncState::Idle) {
+					SyncState::Rounds(round)
+						=> SyncState::Rounds(round.drain(&mut sink, Some(DRAIN_AMOUNT))),
+					other => other,
+				};
+
+				if sink.is_empty() { break }
+
+				for header in sink.drain(..) {
+					if let Err(e) = self.client.queue_header(header) {
+						debug!(target: "sync", "Found bad header ({:?}). Reset to search state.", e);
+
+						self.begin_search(&mut state);
+						break 'a;
+					}
+				}
+			}
+		}
+
+		// check for aborted sync round.
+		{
+			match mem::replace(&mut *state, SyncState::Idle) {
+				SyncState::Rounds(SyncRound::Abort(reason)) => {
+					match reason {
+						AbortReason::BadScaffold(bad_peers) => {
+							debug!(target: "sync", "Disabling peers responsible for bad scaffold");
+							for peer in bad_peers {
+								ctx.disable_peer(peer);
+							}
+						}
+						AbortReason::NoResponses => {}
+					}
+
+					debug!(target: "sync", "Beginning search after aborted sync round");
+					self.begin_search(&mut state);
+				}
+				other => *state = other, // restore displaced state.
+			}
+		}
+
+		// allow dispatching of requests.
+		{
+			*state = match mem::replace(&mut *state, SyncState::Idle) {
+				SyncState::Rounds(round)
+					=> SyncState::Rounds(round.dispatch_requests(|_| unimplemented!())),
+				other => other,
+			};
+		}
 	}
 }
 
@@ -253,12 +321,13 @@ impl<L: LightChainClient> LightSync<L> {
 	///
 	/// This won't do anything until registered as a handler
 	/// so it can act on events.
-	pub fn new(client: Arc<L>) -> Self {
-		LightSync {
+	pub fn new(client: Arc<L>) -> Result<Self, ::std::io::Error> {
+		Ok(LightSync {
 			best_seen: Mutex::new(None),
 			peers: RwLock::new(HashMap::new()),
 			client: client,
+			rng: try!(OsRng::new()),
 			state: Mutex::new(SyncState::Idle),
-		}
+		})
 	}
 }